How do disulphide bonds in hair cause curling?

How do disulphide bonds in hair cause curling?

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I understand that there are several characteristics of curly hair which differ from straight hair (such as an asymmetrical distribution of disulphide bonds in curly hair), but really am struggling to understand the root cause of inherent curl on the macroscopic level.

My current understanding of the hair structure is based mostly upon this website

The most relevant part of the hair for our discussion is the cortex, which is made up of many axially aligned macrofibrils, or macroscopic keratin fibers, which are in some filler essentially of lipids/proteins. Inside these macrofibrils are microfibrils. These are also aligned axially and in some filler of lipids/ proteins. Inside the microfibrils are the protofibrils, even smaller fibers which are twisted around each other like a yarn. These protofibrils are made up of 4 keratin chains which are essentially twisted together and connected by disulphide bonds and hydrogen bonds. While hydrogen bonds are easily broken, the disulphide bonds are not. In curled hair, the macrofibril isn't symmetrical but I am unsure as to how this, or what other effects, actually lead to the curling.

I had previously assumed that the reason for curling is that in an asymmetrical configuration of the hair(IE not cylindrical but more oval in cross section), some residual stresses are formed by the disulphide bonds between the keratin, If this is true, it would lead me to believe that it would cause increased buckling of the protofibrils. But, even with straight hair and more symmetrical disulphide bonds, you already have some curling and buckling of the protofibrils, but the hair doesn't curl on a macroscopic level.

As such, it doesnt seem like this buckling due to asymetrical disulphide bonds would necessarily lead to a curled or organized structure on the macroscale, with the macrofibrils. This leads me to believe I am missing something.

Nice question. I must say it took me many hours to get satisfactory answer.

Hairs are made of keratin molecules, which contain cysteine. Cysteine has thiol (-SH) group, by which it can form disulfide (-S-S-) bond with another cysteine of another keratin, causing bending of hair. See this image from here:

Curling of hair can be justified on both microscopic and macroscopic level.

  1. Microscopic level: See this post from here:

Curly hair has to do with the chemical bonds in the protein that makes up hair - $alpha$-keratin. Keratins, particularly $alpha$-keratin, have long sequences of amino acids (often more than 300) which forms a helical structure.

Pairs of these helical structures then coil about each other in a left-hand coiled-coil structure. These are then attracted to another coiled coil so two keratin helices will stick together. These four-chain structures then associates with another four-chain structure to form the hair filament. One of the amino acids which make up these chains, is cysteine which has a sulpher group which is able to make connections with other sulpher groups on other coiled coils.

The more interactions a filament has with another filament, the more tightly coiled the coiled-coil becomes. Hence, curly hair has more interactions than straight hair. The process of 'perming' hair introduces more accessibility of the sulpher on the amino acid, cysteine, to make these connections. Finger and toe nails have many many bonds between filaments and are thus, very hard.

For example, see how hairs are curled artificially via perming.


This change in location of bonds is what causes curling of the hair (look again at the first diagram and notice the orientation of disulfide bridges). Those vertical strands now get curled due to change in these bonds. Here, the required mechanical tension for bending is provided artificially.

  1. Macroscopic level: Shape of hairs is also determined by its macroscopic structure. Look at this article:

All hair, whether curly or straight, has two major components: the shaft and the follicle. The shafts are the visible, flowing strands that we see on our heads. The follicle is the part of our hair that resides within the skin, or dermis, of our scalp. Each of these structures plays a role in determining our overall hair shape.

Let's start at the root of the issue (pun 100 percent intended): the follicle. It turns out that the shape of our follicles is a major determinant of our hair texture. If you were to look at the follicle of straight hair, you would find it is perfectly round. The follicle of curly hair adopts an oval shape. The flatter the oval is, the curlier the hair will be.

Another contributing factor to a hair's curl is the way the follicle tunnels into the scalp. Follicles of straight hair tunnel vertically down from the skin's surface into the dermis. If the follicle angles into the dermis then the hair will curve as it grows causing it curl. Although, this curving of the follicle can lead to gorgeous curls it causes one major drawback that all curly-haired persons can attest to, dryness. Within the dermis, special glands line the follicle to secrete oil, called sebum, to lubricate the hair. Unfortunately, when follicles curve sebum isn't able to travel the length of the hair as well leading to dryness of hair that doesn't get lubricated.


Although how shape of follicle determines structure of hair strand is probably not known, the major contributing factor likely is how hair emerges from the scalp. When it emerges in a bent shape, it faces a lot of tension from the scalp, which causes it to bend in the shape of the follicle to form curls. Since straight-emerging strands don't face such forces, they do not lead to curled hairs.

In this way, hair curls are a consequence of large number of disulfide bridges between keratin molecules and how the hair emerges from the scalp.

How are disulfide bonds broken in hair?

Under oxidizing conditions, two cysteine molecules (or cysteine residues in a polypeptide or protein) can dimerize through formation of a disulfide bond. Disulfide bonds can be broken by addition of reducing agents. The most common agents for this purpose are ß-mercaptoethanol (BME) or dithiothritol (DTT).

Secondly, can disulfide bonds be broken by heat? Breaking of bonds stabilizing tertiary structure can occur by mercaptoethanol (breaks disulfide bonds), dithiothreitol (breaks disulfide bonds), detergent (breaks hydrophobic interactions), heat (breaks hydrogen bonds), urea (breaks hydrogen bonds), pH (breaks ionic bonds), or chelators (breaks metallic bonds).

Correspondingly, how do you break a disulfide bond in your hair?

In a perm, you don't just break hydrogen bonds, you also break the disulfide bonds that hold the proteins together. You add chemicals that break the disulfide bonds (bonds between sulfur atoms). Then you reshape your hair and add chemicals that reconstruct those disulfide bonds, holding your hair in a new shape.

Why is it harder to break disulfide bonds than hydrogen bonds?

Disulfides are covalent and more stable than the others. Absolute strength depends on how you look at it. It is a relatively weak and easily broken covalent, but it is stronger than any single hydrogen or hydrophobic interaction. However, the collective strength of those bonds is greater in most proteins.

Hair Biology & Bonds

Your hair is composed of keratin, a strong fibrous protein, and is built from cells similar to those of your skin. The average number of hairs on the human scalp is 120,000, although blondes tend to have more and redheads less. Hair is a remarkable fibre.

A healthy hair can stretch up to 30% of its length, can absorb its weight in water and swell up to 20% of its diameter. A single scalp hair can hold a weight of 100g and an average head of hair twisted together can support 23 tons. However, this is only if your hair is in good condition!

Disulphide and Hydrogen Bonds

‘Disulphide bonds are one of the strongest naturally-occurring bonds in nature.’ The protein structures of the hair shaft are held together by chemical bonds called disulphide and hydrogen bonds.

While the curliness (or straightness) of your hair depends on the shape of the follicle, it’s the disulphide bonds that keep the hair in the shape it was formed, and they can only be altered by perming or relaxing.

Disulphide bonds also give your hair its elasticity and strength. Hydrogen bonds, on the other hand, are easily broken by the application of water and can be temporarily reset with heat until they become wet again (either from washing or humidity).

Hydrogen Bonds

These bonds are the most flexible. I have touched on this in my 3 part ‘Frizz’ series. Hydrogen bonds are easily broken in the presence of water and heat. They are the primary bonds responsible for changing our hair’s overall shape. They are responsible for up to 30% of the strength and up to 50% of its elasticity. When the hair is wet by either shampooing/conditioning or in the presence of humidity, the molecules that enter the fiber move in and break up the hair’s preset hydrogen bonds and form new ones.

Hydrogen bonding allows our hair to change shape temporarily and produces a strong hold. Here is an example of hydrogen bond manipulation resulting in an altered appearance of the hair: setting your hair in rollers. Hair is usually set in rollers while wet. The hair is then held in position until it dries. As the hair dries, hydrogen re-bonding occurs, but in the new “shape”.

When we wet our hair, these bonds are temporarily disrupted and we’re able to take advantage of the hair’s flexible hydrogen bonding arrangement to restyle our hair with more definition. So the hair will remain in the new “shape” until it’s presented with water again and that can either occur through shampooing/conditioning or humidity. Hydrogen bonding is the reason why hair frizzes and curls fall and why we’re able to manipulate our hair into a range of hairstyles. Other examples of hydrogen bond manipulation: twists outs and using a flat iron.

(Hair Structure and Chemistry Simplified. "Chemical Composition of Hair” in Texas Collaborative: A Closer Look at the Properties of Hair and Scalp. “Fundamental Properties of Afro-American Hair as related to Their Straightening/Relaxing Behaviour”. The Science of Hair Care).

How To Strengthen & Repair Hair Bonds

Hair bonds are what makes up your hair’s structure and texture. They also determine the strength of your hair so it’s important to look after them properly and treat them for any damage if necessary.

What Are Hair Bonds?

Hair is made of keratin and there are three different types of hair bonds that form and hold this structure together.

  • Disulfide Bonds : These are permanent hair bonds that create your hair’s texture. The amount of disulfide bonds within the hair determines how curly the hair is - the more bonds the curlier the hair. Disulfide bonds are largely responsible for how strong our hair is and how prone it is to damage. But, disulfide bonds themselves can be damaged by bleach and chemical treatments.
  • Salt Bonds : These bonds are created between the positive end of one amino acid chain and the negative end of another. They are responsible for approximately one third of the hair’s strength. These salt hair bonds can be damaged by sudden pH imbalances which can be caused by something as simple as using hair products that are unsuitable for your hair type.
  • Hydrogen Bonds : Unlike disulfide bonds, hydrogen bonds are temporary and can be ‘reset’ by water. The water breaks older hydrogen bonds and forms new ones. These hair bonds are also responsible for your hair’s elasticity allowing for our hair to change shape like when using heated styling tools. Hydrogen bonds are the primary reason our hair sometimes becomes frizzy and can be damaged by both moisture overload and heat.

All of these hair bonds help your locks stay strong and manageable so it’s important to look after them. But if they do become damaged there are ways to repair them!

How Hair Bonds Become Damaged & Broken

Many things in our day to day lives can cause hair bonds to break. Disulfide bonds can be damaged by coloring your hair, swimming in chlorinated water, and using chemical treatments like bleach or relaxants. Hydrogen bonds are broken by water entering the hair, whether it’s from your wash routine, or the humidity in the air. If you style your hair in one humidity then move to another, the hydrogen bonds will again break and reset causing hair to lose its original shape. They can also be broken by heat from blow drying or styling with hot tools. Salt bonds are affected by pH levels, so they break when they experience sudden pH imbalances, like when you use products whose pH is not optimized for the scalp.

Strengthen & Repair with The Curlsmith Hair Bond Builder

When it comes to looking after our hair bonds we should try to minimise things that can damage them in the first place. Many things, from heat to bleach, can damage these bonds and affect our hair strength. However, for bonds that are already damaged, using a hair bonding treatment can help restore the strength and integrity of the hair and its bonds, giving you soft, luscious locks once again.

Our Bond Curl Rehab Salve is a bond builder that contains some curl-loving proteins. It works by targeting hair bonds to re-link and repair damage, strengthening the hair from the inside out and protecting against breakage. It leaves the hair super soft and manageable, as well as working to enhance your natural curl pattern. This formula will work with any hair type, however those with damaged or high porosity hair will need to use it more often alongside other products from our hair strength range . As this product is not a conditioner, it should be followed by using a shampoo and a conditioner.

Whilst damaged hair bonds need protein rich treatments to be repaired, if you use them too often you can suffer from protein overload . This is when your hair has too much protein, and can be easily repaired by clarifying to remove excess protein and treating with a moisturizing deep conditioner.

How Does Our Bond Curl Technology Work?

Our Bond Curl Rehab Salve is a powerful blend of superfoods and patented active ingredients that targets hydrogen, salt, and disulfide hair bonds to repair, rebuild and restore hair fiber strength. It also provides protection to help against further damage. The Bond Curl helps achieve this thanks to the following technology:

Cureplex Di-Sulphide Re-Bonding Treatment:

M i nd Y our L ook uses this definition for healthy hair:

"Hair is healthy when it's thickness is uniform from root to end."

Di-Sulphide Bonds

The thickness of your hair is determined by the health of its under-layer & keratin.

At the start of a strand's life cycle, keratin is produced with a uniform thickness from root to end.

The thickness & body of your hair is determined by the existence of bonds between two converging protein chains. Where these bonds are broken, uniformity is lost.

The key atom in the composition of keratin is Sulphur, specifically, it's electrons.

These Sulphur electrons are responsible for each protein chain being able to form a bond with one another.

The Strength of Atomic Bonds

The bonds in keratin bind at a sub-atomic level.

It is due to this relationship in its makeup that scientists term this specific bond as a Di-Sulphide bridge or Di-Sulphide bond, using S-S bond for short.

If you had any doubt as to the strength of the Di-Sulphide bonds, Philip Kingsley Clinics of London & New York (Accessed 28 Dec 20, state that:

. "Disulphide bonds are one of the strongest naturally-occurring bonds in nature.".

. "A healthy hair can stretch up to 30% of its length, can absorb its weight in water and swell up to 20% of its diameter. A single scalp hair can hold a weight of 100g and an average head of hair twisted together can support 23 tons. However, this is only if your hair is in good condition!"

When these bonds are broken, it may occur gradually and its effect may be so subtle that it goes unnoticed over time.

However, the cosmetic impact from undergoing a Cureplex Di-Sulphide Re-Bonding Treatment is comparatively dramatic, as your hair is repaired in a vastly shorter time period as well as being repaired on mass.

Damaged Hair

So if Keratin Di-Sulphide bonds are that strong, what could possibly break them?

Keratin Di-Sulphide bonds are broken by:

  • Heat - Energy
  • U/V & other forms of radiation - Energy
  • Bleach Bloating - Tension Stress
  • Keratin Straightening Agents - Chemical Reaction
  • Oxidation - Sub-atomically / Organically

Free Radicals

M ind Y our L ook uses this definition for a free radical:

"A free radical is an atom with one or more unpaired electrons in its outer shell."

Where do They Come From?

Free radicals are formed due to exposure of your body to:

Free radicals also form naturally as a bi-product of your body's normal metabolic processes.

What Do Free Radicals Do?

Free Radicals Are Unstable Atoms

Stable atoms are made of a central nucleus containing at least one proton (+), and an equal number of orbiting electrons (-).

Electrons are grouped by shells, with each shell containing 2 in its first, then 8 per shell until it's last outward shell.

The outer shell interacts with other atoms to become part of bigger structures known as compounds.

Where the number of both positively and negatively charged components of an atom are the same, it is considered to be less reactive (stable) than those that do not.

Atoms that have an unequal (unstable) number of electrons to protons, exist in a constant state of electrical chemical imbalance.

Forces of nature are constantly exerted on these atoms to become stable.

Opposites Attract

You've probably seen what happens when opposite poles of two magnet are slowly moved closer to one another.

When close enough, they snap together. The situation with free radicals is similar.

The instability resulting from an unpaired electron is based in its overall positive or negative charge.

The unstable charge is of such force, that the free radicals literally pull electrons from the outer shells of anything else with weaker structural integrity, such as keratin cells.

Oxidation by Free Radical


M ind Y our L ook uses this definition for oxidation by free radical:

"Oxidation by free radical describes the transfer of electrons from one set of atoms (keratin) to another set (free radicals)."

When free radicals are present, there is a high risk that your keratin will undergo oxidation by free radical.

Where the electrical chemical difference between your keratin and a free radical is great enough, the electrons that would otherwise create Di-Sulphide bridges, shoot off from the Sulphur atoms, stabilising the free radical.

This is how the Di-Sulphide bonds are broken and how your hair is damaged when your keratin undergoes oxidation by free radical.

As such, your hair will no longer have the same thickness from root to end and the strength of your hair will diminish.

Fewer bonds translates into hair that appears damaged, aged and unhealthy.

There is also much less that you can do with structurally damaged hair as it more easily breaks and is more susceptible to jellification in bleaching processes.


What Anti-oxidants Do

You may have heard of anti-oxidants.

Anti-oxidants act as free electrons, reducing the local impact of an oxidative state.

When anti-oxidants are introduced into an environment of oxidation (or reduction), they have a relatively weak electrical chemical resistance compared to Sulphur electrons. This is because Di-Sulphide electrons already form part of those atoms.

Electrical Chemical Difference

To compare the two interactions, we would look at the scale of electrical chemical difference required for a Di-Sulphide bonded electron vs a free electron to be drawn into a state of oxidation.

On the Sulphur side, we have an electron that is already part of an atomic system. It is in orbit of a nucleus, bound by the mutual forces of attraction. On the free electron side, we have an electron that is unbound to any atomic structure.

As a force of attraction between the Di-Sulphide electron and it's nucleus exists, when comparing it to any resistive force exerted by a free electron, the Di-Sulphide electron has the advantage.

The reason for this advantage is due to the fact that, if the free electron is more easily drawn into a state of oxidation by the free radical, any state of oxidation that the Di-Sulphide electron might have experienced had the free electron not existed, occurs prematurely.

The required relative strength of the electrical chemical difference to oxidise free electrons by free radicals is much lower than that required to disturb your keratin's Di-Sulphide bonded electrons.

How Free Electrons Cancel Out Oxidation by Free Radical

Consequently, where there are sufficient free electrons to pair with the unpaired outer shell electrons of free radicals, the local effect of oxidation on your hair's health is essentially nullified.

Where free radical unpaired electrons no longer have that status of unpaired electron, they become stable, and their contribution to the oxidative state ceases.

Simply put, the main benefit of anti-oxidants is that your hairs' cells remain undisturbed and healthy.

Anti-oxidants can be found as natural supplements in drinks such as green tea or additives in isotonic waters.

The Cureplex Di-sulphide Re-bonding Treatment

Damage Reversal

The combination of these Di-sulphide Re-bonding Treatments reverse the impact of damage to your hair, inherent in any oxidation by free radical.

These treatments allow keratin to re-bridge their broken S-S bonds.

Your hair will look years younger, present with more body and feel healthier. You will be surprised at the response your hair shows after this treatment.

If damage to your hair was solely linked to the solar radiation exposure that we experience daily, thanks to the hole in our ozone layer, this treatment will be of benefit to you.

If you're regularly exposed to carcinogens, as most of us are, but even more so if you're a smoker, this treatment is a must considering the marginal investment of this treatment as a percent of your overall hair services investment.

As you are reading this resource, it is likely that you are a person that either values the health of their hair, or at least invests in it, as if they do.

And if you do regularly invest into your hair and it's cosmetic wellbeing, make the choice to bring this treatment into your ongoing use.

But if not, you owe it to yourself, and for all of those hair services that cost you in recent years, to give it a go, at least just once.

For then, you have a chance that future investments into your hair can earn back some of the value that has been lost.

Otherwise . it's a little bit Alanis Morrisette . don't you think?

No. 1 Bond Creator
  • Is an in salon treatment
  • applied during the bleaching or colouring process
  • benefits: damage prevention, restores Di-Sulphide bonds
No. 2 Bond Fortifier
  • Is an in salon treatment
  • applied to hair after any colour service
  • benefits: leaves hair feeling and looking healthy, young & manageable

After Care:

No. 3: Bond Sustainer
  • after care solution to extend the longevity of the bond creator
  • apply treatment twice weekly, leaving in 2-3 mins
  • benefit: extends the effectiveness of the No. 1 & No .1 treatments & is a bond booster.
Cureplex Shampoo & Conditioner
  • enjoy the full benefits when using the Cureplex shampoo & conditioner every wash
  • anti-ageing & colour fade defence
  • will not only nourish, strengthen and add elasticity, but also adds a frizz free finish
  • specifically created to complement this treatment.

Redeem Your Free Sample Treatment Pack

You got to this point and so I would say that you've definitely earned it.

Let us know by registering your details in the form below to receive an email confirmation of eligibility for a FREE Cureplex Di-Sulphide Re-Bonding Service & Treatment Sample Pack:

6 thoughts on &ldquo How Does Heat Styling Hair Work and Why Is My Hair the Way It Is? &rdquo

Taylor, thanks for sharing your hair care with me! Here’s a great article that can answer all of your questions on chemical straightening/relaxing!

Basically, what chemical straightening products do, is relax eliminate some of the disulfide bonds in your hair follicles relaxing the curliness of your hair.

That is a fun fact! Thank you for sharing that with me. I actually wondered about that.

Thank you for your great comment and questions Alexandra! This blog post was supposed to give the analysis of hair straighteners (sorry that I didn’t put that clearly and that my photo was misleading). However, here’s a link that I think can really help answer all of your questions!

Also, through all of the research I did on this topic, I saw that blow drying in fact causes less damage due to the heat being blown through and around hair strands. Even though it’s being blown onto hair in a reasonably direct manor, it is nowhere near as direct as a straightener or curling iron which has hot plates or barrels that sit on the hair strands themselves. As for wands and curling irons, the article above discusses those!

Here’s also another great article that can answer all of your hair repair questions!
I unfortunately cannot say whether or not deep conditioning treatments mask the hair or replenish the cuticle off hand.

I’m African American and my hair is naturally curly but I use a relaxer, which straightens it chemically. I’ve always wondered whether or not that was slightly better than using heat. I still have to use a straightener after I relax my hair because the relaxer only straightens my roots, but my ends are wavy/frizzy. I’ve also gotten bleach blonde highlights last year and I’ve gotten a lot of breakage. I’ve done research on how to care for bleached hair and it mostly includes deep conditioning.

I hear that having curly hair is much drier than straight hair and more susceptible to damage. I looked it up and apparently because of the texture, the oil from the scalp has a difficult time making it all the way down the strands. There for you probably should dye or straighten it. ….But I do! Last week when I was getting my hair highlighted for the 50th time in my life I had a plethora of questions for my stylist. One was how easy is it to go back to being a brunette after being blonde for so long. She said it takes a couple of colorings because the follicles have been opened by bleaching and they need time to close in order for the color to stick. Fun fact.

Very scientific analysis of hair care, I loved it! I, myself, have very naturally curly hair and try not to straighten it more than 2-3 times a week. I do wonder though, what about the affect of blowdrying? You spoke about ceramic straightening but not about the blow drying process. Would this be considered even more harmful even though it does not have direct contact with the hair cuticle? Also, what about curling irons and wands, since they are on the hair much longer than a straightener is? Are they more dangerous? I used to have very damaged hair but I did find some deep conditioning that worked for me. Do you know if they actually repair the cuticle or simply mask it with an oil based polymer?

The Scientific Processes During Perming & Relaxing

As we know, the hair is made up of protein chains held together by series of physical and chemical bonds which give the hair its shape and strength. The bonds we are most concerned with in styling the hair are the side bonds.

Side bonds are found in two forms – physical side bonds and chemical side bonds. Breaking and reforming these side bonds allow us to rearrange the wave pattern of the hair. Physical side bonds can be broken using heat and water and reform when the hair dries and/or cools.

However, this article is about perming and relaxing and the scientific processes that occur. When the hair is permed (and sometimes when straightened) the disulfide bonds (the chemical side bonds) of the hair are broken through a chemical reaction called ‘reduction’. A reduction reaction involves either the removal of oxygen or the addition of hydrogen. In the case of permanent waving, the reduction is due to the addition of hydrogen.

The disulfide bonds join one sulfur atom on one polypeptide chain to another sulfur atom on different polypeptide chain. Perms use reducing agents called thiol compounds, which break the disulfide bonds by adding a hydrogen atom to each of the sulfur atoms in the disulfide bonds. With the disulfide bonds broken, the polypeptide chains are able to slip into their new shape.

The broken disulfide bonds are reformed through the neutralization of the thio compound used to break them. The most common neutralizer is hydrogen peroxide and the chemical process that removes the hydrogen atoms and reforms the disulfide bonds is called “oxidation”.

Oxidation can result in the lightening of the hair color – especially if a strong thio compound was used – and this is why the hair should be rinsed carefully and blotted thoroughly before applying the neutralizer. The oxidation reaction combines the hydrogen and oxygen atoms in the peroxide molecules with the hydrogen atoms used to break the disulfide bonds to form two separate molecules of water. (Peroxide + Hydrogen + Hydrogen = Water )

The removal of the hydrogen atoms from the sulfur atoms forces them to reform their disulfide bonds in the new shape (around the perm rods). The process is the same for relaxers and straighteners that use thio compounds, except that these are removing curl rather than creating it.

Hydroxide relaxers break the disulfide bonds in the hair by removing one atom of sulfur from the disulfide bond and thereby converting it into a lanthionine bond. This process is called lanthionization. When a hydroxide relaxer breaks a disulfide bond the bond is permanently broken and can never be reformed.

Hydroxide relaxers leave the hair extremely alkaline even after rinsing. To restore the pH balance of the hair an acid-balanced shampoo or normalizing lotion neutralizes any remaining hydroxide ions to lower the pH of the hair and scalp. Some neutralizing shampoos intended for use after hydroxide relaxers have a built-in color-change indicator to show when the hair’s pH has returned to normal.

The neutralization/normalizing process with hydroxide relaxers never uses any oxidation, in fact, oxidizing agents can seriously damage hydroxide relaxed hair.

How Things Work: Hair-straightening

As surprising as it may sound, cosmetics and styling often involve a large amount of science. Whether it be producing safe makeup or coming up with effective shampoos and moisturizers, science is everywhere. Hair straightening is one such technique that relies heavily on the basic scientific properties of hair.

Hair is made up of a protein known as keratin. Keratin is composed of long chains of amino acids. Along with hair, nails and teeth enamel are also made up of keratin. Hair, nails, and teeth have one important factor in common — they are all strong.
It is extremely difficult to break a strand of hair apart without a pair of scissors. No amount of twisting, pulling, rubbing, or even hammering can do anything to hair.

The strength of hair can be attributed to a special property unique to proteins like keratin, which are made up of a large number of sulfur-containing amino acids. Sulfur atoms, from adjacent chains of keratin, bond together to form disulphide bonds. These extra bonds make the fibers that have keratin very strong. In addition, they ensure that the position of the keratin molecules remains fixed, such that the shape of the hair fiber stays the same.

Naturally, this is a good property since hair — especially long hair — is normally subjected to a large amount of stress, and one would not want hair breaking or changing its shape because of this everyday wear and tear. However, when people do want to change the shape of their hair — get rid of curls, add curls, make it wavy, make it straight — these disulphide bonds pose a great problem. Most hair-straightening techniques, therefore, target these bonds. An easy method of breaking these bonds is using heat. This brings us to what is probably the most common technique for straightening hair — the flat iron.

The plates of the iron are usually heated to high temperatures, generally between 300 and 500 degrees Fahrenheit.
When hair is passed through the iron quickly, while being held tight and straight, the extreme heat causes the disulphide bonds to break. This breakage allows the keratin chains to move around slightly and assume a position that results in straightened hair. When the hair cools down, the disulphide bonds between the keratin are reformed. Because the keratin molecules are in different positions when the bonds are reformed, the hair stays in the straightened shape for a long period of time. As most people who use flat irons know, this method of straightening hair is not permanent.

Exposure to moisture causes the hair to revert back to its original shape. Permanent hair straightening techniques use harsher methods, with chemicals, to break the disulphide bonds and reform them. The disulphide bonds cannot be broken apart by oxidizing agents, which are acids, but can be broken apart by strong reducing agents, which are bases. Alkaline solutions, therefore, are applied to hair to break apart the disulphide bonds. The hair is then held straight and acidic solutions are applied to it.

The acid neutralizes the base, stopping the disulphide bond cleavage reaction and allowing the disulphide bonds to reform in new positions. Although all chemical hair-straightening techniques have this same basis, each has a slightly different mode of action on the hair. Alkaline hydroxides are the harshest and most rapid agents for breaking the disulphide bonds usually, either sodium hydroxide or calcium hydroxide is used for this purpose. Along with breaking the disulphide bonds, these solutions also cause the hair to swell. Since they are so harsh, these chemicals should not be left in the hair for more than 10 minutes, as they can cause severe damage to the hair and scalp if not used properly. Hair is usually treated with a cream to protect it from the caustic effects of these chemicals before applying the alkaline hydroxides. Thoroughly washing off the solutions allows the reaction to stop and the disulphide bonds to reform, sealing the hair in its new, straightened position.

Solutions containing thioglycolate are safer to use. Thioglycolate has a rather unpleasant odor, but since it is much less harsh than alkaline hydroxides, it is a more popular method for hair straightening. Thioglycolate contains a thiol (-SH) group, and dissociation of the hydrogen atom from the sulfur creates a thiolate (-S-) ion. Thiolate ions are good reducing agents and help break the disulphide bonds. This method generally takes much longer than alkaline hydroxides. Also, a strong oxidizing agent, such as hydrogen peroxide, has to be applied after thioglycolate treatment in order to stop the reaction and help the bonds reform.

Another method is the use of bisulphate-containing solutions. These, too, can act as reducing agents. They work slightly better than thioglycolates and are safer than alkaline hydroxides. Although chemical hair straightening techniques are popular, scientists are now trying to come up with a way to attack this issue from its roots.

According to a November 2005 article on the Telegraph, scientists from L’Oreal in Paris discovered that a curve-shaped hair follicle gave rise to curly hair while a straight one gave rise to straight hair. The article further states that by understanding what process in the body determine the shape of the hair follicles, scientists could develop a drug to alter the shape of hair follicles and, ultimately, hair. As of now, no such pill exists, and flat ironing or using chemicals are the only two ways to straighten curly hair.

Other Ways to Heal Damaged Hair

Protein Treatment

Hair is essentially made of protein (keratin), so a temporary fix is to add in more protein to support and strengthen the hair. Protein treatments work temporarily to fill in the gaps of the outer layer of the hair cuticle (bond repair treatments go to work in the inside of the hair, the cortex) and fill in the gaps with protein to strengthen hair. It is recommended to to do them every 4-6 weeks, as everyday wear and tear and products can reduce the protein in our hair.

Don’t Be Afraid of Protein!

I’ve talked to many women who are afraid to use protein at the first sign of wonky, frizzy, uncooperative hair. Protein overload can be an issue when too much protein is used, say, one or twice a week. I really encourage you to throw that fear aside, yes, even for low porosity curly girls. Even they need protein – not as often or as much as those with high porosity hair, but it is still needed from time to time. And then pay close attention to how your hair responds to the treatments to see when you need to do one again.

There are three different types of protein treatments that I’ve used they have all greatly helped my hair! My recommendation is to do just one treatment and see how your hair responds.

    – this can be made from the gelatin packets at the grocery store. Super cheap and easy! This post explains how to know when you need a protein treatment. This treatment saved my hair from hygral fatigue! It works really well. It is made mostly from gelatin. (I don’t use the second step because it contains silicones which build up on the hair and prevent moisture from getting in) – you can actually make a protein treatment from the rice water! The protein molecules in rice are larger than gelatin so therefore, they do not penetrate the hair cuticle as easy. So this is less strong and effective than gelatin. If you try a rice water rinse and it doesn’t help much, I highly recommend doing a gelatin rinse and see how your hair responds.

Both Protein and OlaPlex

You can use both in conduction with one another! OlaPlex even recommends it on the bottle. Bond repair treatments and protein perform different functions and have different ingredients, so your hair can benefit from both.

When I first started doing the Curly Girl Method, I did one protein treatment a week for one month and one OlaPlex treatment a week for a month. Then I backed off of the protein because I could tell my hair was strong and needed a break (it was getting a little hard and stiff), and just did OlaPlex twice a month. I do protein on an as-needed basis now. My hair is continually getting much healthier, shinier, bouncier and softer, so I’d say this plan has been working!

We are all different, so I can’t say that my plan will work for you, but it could give you a starting point at least.

Cut off the Damage

For some of us, hair can get so damaged that it’s irreversible. I know, sad day! Chemical straightening can really do an awful number on hair, as can bleaching and coloring. This happened to me – I was coloring my hair at home and because I didn’t really know what I was doing, I kept pulling the color out about four inches inches each time I did it. So I was coloring on top of color each time, and it caused major damage to my hair! After doing the Curly Girl method for four months, I had the damaged ends cut off. It’s called a Big Chop and I wrote about it in this post!

Deep Conditioning

Curly hair especially needs lots of hydration, so deep conditioning (with a heat cap such as this one) is how I heal my hair, along with the protein and OlaPlex treatments. I have seen my hair go from very frizzy, not lasting more than one day after washing, to getting rid of most of the frizz and going for 4-5 days in between washes in just 6 months! In this post, I share why deep conditioning is so helpful and what my routine has been!

Watch the video: Disulfide Bond Formation (August 2022).