What Really Happens to Your Hair During Relaxers, Keratin, Silk Amino & Japanese Straightening Treatments?
Relaxers, keratin treatments, silk amino treatments, and Japanese straightening can ALL make your hair look straighter but what they’re doing INSIDE your hair is completely different. Let me show you what’s actually happening to your cuticle, cortex, and bonds.
This distinction matters because we often group chemical and smoothing services together based on the final result: straighter, smoother, shinier hair.
But two treatments can create a similar-looking result while affecting the hair fiber in completely different ways.
Some treatments permanently change the internal structure of the hair. Others primarily smooth the surface, interact with proteins, reduce frizz, or temporarily reinforce damaged areas.
To understand the difference, we first have to understand the hair itself.
First, Let's Go Inside the Hair Strand
A hair strand has multiple structural components, but for understanding chemical straightening and smoothing treatments, we're going to focus primarily on two: the cuticle and cortex.
The Cuticle: The Protective Outer Layer
The cuticle is the outer protective layer of the hair fiber. Its overlapping scales help regulate friction, porosity, moisture movement, shine, and access to the inner portions of the hair.
In simple terms: Think of the cuticle like the roof shingles or protective jacket of your hair.
When those scales are relatively smooth and intact, the hair generally reflects light better and feels smoother. When they're raised, damaged, worn away, or highly porous, hair can feel rough, dry, tangled, or frizzy.
But here's something important: the cuticle isn't where most of your hair's permanent natural shape is determined.
For that, we need to go deeper.
The Cortex: Where the Structure Lives
The cortex makes up much of the inner structural body of the hair. It contains keratin proteins and many of the chemical bonds responsible for the hair's strength, elasticity, and shape.
In simple terms: The cortex is the inside of the hair where much of its strength and natural shape live.
If we're talking about permanently changing someone's natural texture, we're no longer talking only about making the outside of the hair feel smoother. We're talking about chemistry affecting the structural organization inside the hair.
And that's where bonds become extremely important.
The Bonds You Need to Understand
There are several types of chemical interactions within hair, but three commonly discussed in cosmetology are disulfide bonds, hydrogen bonds, and salt/ionic bonds.
Disulfide bonds are strong covalent bonds associated with cystine in keratin. They contribute significantly to the structural stability and shape of the hair.
Think of these as some of the hair's heavy-duty connections. Permanently altering these connections can permanently alter the treated hair's texture.
Hydrogen bonds are much weaker and can be disrupted and re-formed through water and heat.
This is why someone with curly hair can blow-dry and flat-iron their hair straight, but after exposure to enough water or humidity, the hair can move back toward its natural configuration.
Salt or ionic bonds are influenced by pH and the electrical charges present on protein groups.
In simple terms, very acidic or alkaline environments can change how some of these interactions behave.
Now that we understand the cuticle, cortex, and bonds, we can see why these four services are NOT interchangeable.
Relaxers: Permanent Structural Change Through Chemical Conversion
A traditional hydroxide relaxer is a permanent chemical texture-altering service.
It doesn't simply coat curly hair and make it appear straight. Its chemistry reaches the cortex and permanently changes part of the hair's internal structure.
What Happens at the Cuticle?
Hydroxide relaxers are strongly alkaline.
The high pH causes the hair fiber to swell and increases cuticle permeability, allowing the chemical to penetrate deeper into the hair and reach the cortex.
In simple terms: The relaxer needs to get inside the hair to permanently change its texture.
The alkaline environment causes significant swelling and allows the relaxer to reach the internal structure.
This is also one reason relaxed hair has to be handled carefully. We're not simply applying a conditioner to the outside of the strand. We're intentionally creating a chemical reaction within the hair fiber.
What Happens Inside the Cortex?
This is where the major transformation occurs.
Hydroxide relaxers permanently alter the cystine/disulfide structure of keratin. A key reaction associated with hydroxide relaxing is called lanthionization.
During this process, some cystine structures are chemically converted into lanthionine-containing structures.
In simple terms: A relaxer goes inside the hair and permanently changes some of the strong structural connections associated with the natural curl pattern.
It's not simply "loosening" the curl until the next shampoo.
The chemistry of that treated section has been changed.
That's why shampooing relaxed hair doesn't restore that section to its original natural curl pattern.
New growth comes in with the client's natural texture because that new hair was never exposed to the relaxer.
This is also why relaxers require new-growth touch-ups rather than repeatedly processing the entire strand.
Relaxer in One Sentence
Natural structure → alkaline swelling and penetration → permanent alteration of cystine/disulfide structure through lanthionization → treated hair remains permanently altered.
Keratin/Smoothing Treatments: It's More Complicated Than "Coating the Hair"
Keratin treatments are where terminology gets tricky.
That's because "keratin treatment" is a marketing category, not one single chemical reaction.
Two products can both be marketed as keratin treatments while using different active ingredients and producing different degrees of smoothing or straightening.
What Happens at the Cuticle?
Keratin/smoothing treatments commonly deposit conditioning ingredients, proteins, amino-acid-derived materials, polymers, and other ingredients around the hair fiber.
Combined with blow-drying and flat-ironing, the process can create a smoother, lower-friction surface and make the cuticle behave more uniformly.
In simple terms: Imagine rough roof shingles becoming smoother and more organized.
A smoother surface reflects light better, which contributes to shine. The strands also experience less friction against one another, which can translate into less frizz, fewer tangles, more slip, and a silkier feel.
What Happens Around or Inside the Cortex?
This depends heavily on the actual chemistry.
A typical smoothing system is not performing the same lanthionization reaction as a hydroxide relaxer.
Depending on its active ingredients, however, heat and reactive compounds can produce chemical interactions or crosslinking with hair proteins that help maintain the fiber in a smoother or straighter configuration.
So the statement that "keratin treatments just coat the hair" is too simplistic.
Some formulas involve chemistry beyond simple surface deposition.
At the same time, we shouldn't assume every product labeled "keratin" is doing exactly the same thing internally.
In simple terms: A keratin treatment and a hydroxide relaxer aren't taking the same chemical road.
The relaxer permanently converts part of the hair's structural chemistry.
A smoothing treatment can use heat and other chemical interactions to make the hair smoother and straighter, but the exact mechanism depends on the formulation.
Unlike a hydroxide relaxer, the cosmetic smoothing effect of many keratin systems gradually diminishes through shampooing, environmental exposure, and normal wear.
Keratin/Smoothing in One Sentence
Hair fiber → treatment chemistry + heat → smoother surface and formula-dependent protein interactions → reduced frizz, increased shine and varying degrees of temporary-to-semidurable curl reduction.
Silk Amino Acid Treatments: Conditioning Is Not the Same as Permanent Straightening
The term "silk amino treatment" also requires some clarification.
Silk proteins can be hydrolyzed into smaller peptides and amino-acid-containing materials that can function as conditioning and film-forming ingredients in hair products.
But seeing the words silk, amino acid, or protein on a bottle does not automatically tell you the entire chemical mechanism of the treatment.
What Happens at the Cuticle?
Hydrolyzed silk and other protein ingredients can deposit on damaged or porous areas of the hair fiber, helping improve surface smoothness and reduce friction.
Smaller protein fragments may interact with more porous areas of the hair, while larger materials tend to remain more surface-oriented.
In simple terms: Imagine damaged hair like a road with cracks and potholes.
Protein-containing ingredients can temporarily deposit around damaged or porous areas, making the surface feel smoother and more uniform.
But this doesn't mean we've created brand-new virgin hair.
A protein treatment isn't literally growing new cuticle scales onto damaged hair.
It can improve how damaged hair feels and behaves, but that's different from reversing all structural damage.
What Happens Inside the Cortex?
A straightforward silk amino/protein conditioning treatment does not permanently break the disulfide bonds responsible for maintaining the hair's structural configuration in the way a permanent chemical straightening service does.
It may improve feel, manageability, surface properties, and temporarily reinforce compromised areas through protein interactions.
But conditioning damaged hair is different from permanently rearranging its structural bonds.
In simple terms: Silk amino acids themselves aren't doing what a relaxer does.
Hair can feel smoother, stronger, shinier, and healthier without its natural curl structure being permanently changed.
And this creates an important question:
What if something marketed as a "silk amino treatment" dramatically straightens highly textured hair and keeps it significantly straighter for months?
Then you need to look beyond the marketing name and examine the actual active chemistry of the complete formula.
The dramatic straightening may not be coming from the silk amino acids themselves.
Silk Amino in One Sentence
Porous/damaged fiber → protein/amino-acid interactions and deposition → smoother, more conditioned surface and temporary reinforcement → generally no permanent texture conversion from the silk amino ingredients themselves.
Japanese Straightening: Reduce, Reshape, Re-Form
Japanese straightening, commonly called thermal reconditioning, is another permanent texture-altering service.
However, it doesn't accomplish permanent straightening through the same reaction as a hydroxide relaxer.
Japanese straightening systems commonly use reducing chemistry such as ammonium thioglycolate or related thioglycolate systems, followed by controlled heat and an oxidizing neutralization step.
Think:
Reduce → reshape → re-form.
What Happens at the Cuticle?
The reducing solution needs to penetrate through the protective outer portion of the hair to reach the cortex.
Depending on the formulation and pH, the hair becomes swollen and more permeable, allowing the reducing chemistry to access internal keratin structures.
In simple terms: We need to get the chemical inside the hair because that's where the structural bonds we're trying to manipulate are located.
This also explains why the starting condition of the hair is extremely important.
Hair that is already highly porous, heavily bleached, chemically compromised, or structurally weakened may have a greater risk of additional damage when exposed to reducing chemistry and high-temperature thermal processing.
What Happens Inside the Cortex?
The reducing agent reduces a portion of the disulfide bonds between cystine residues within keratin, producing sulfhydryl/thiol groups.
In simple terms: Remember those heavy-duty connections helping maintain the hair's structure?
The reducing step temporarily disconnects some of those connections so the hair can be reshaped.
Imagine the natural curl structure being held together by strong connectors.
The first chemical step essentially says:
"We're temporarily disconnecting some of these so we can reposition the structure."
Why Is the Flat Iron So Important?
After the reducing stage is appropriately processed and rinsed, the hair is dried and carefully flat-ironed into a straight configuration.
Heat also changes hydrogen bonding and helps physically align the fiber into the desired shape.
This means the flat iron isn't simply being used to make the finished hair look shiny.
Heat is part of the restructuring process.
In simple terms, the chemical creates the opportunity for restructuring, and then the stylist physically positions the hair:
"THIS is the new shape we want."
Then Comes Oxidation
An oxidizing neutralizer is applied after the hair has been positioned into its straighter configuration.
Oxidation allows many of the reduced sulfur groups to form disulfide linkages again.
So instead of:
Disconnect → straighten → get the hair wet → curl immediately returns
the process is closer to:
Reduce/disconnect → physically straighten → oxidize/re-form bonds while the hair is in its new configuration.
That is why Japanese straightening is a permanent texture-altering process on the treated portion of the hair.
When new hair grows from the scalp, that new growth still has the person's natural texture because it hasn't undergone the chemical process.
Japanese Straightening in One Sentence
Natural structure → reducing chemistry penetrates cortex → disulfide bonds reduced → hair thermally reshaped straight → oxidation allows bonds to re-form → treated hair remains permanently straightened.
Relaxer vs. Japanese Straightening: The Critical Difference
This is one of the most important distinctions to understand.
Both services can permanently straighten hair.
But they do not use the exact same chemical reaction.
Hydroxide Relaxer
Cystine/disulfide structure → lanthionization → permanent chemical conversion
Japanese/Thioglycolate Straightening
Disulfide bonds → reduction → physical straightening → oxidation → bond re-formation in the new configuration
In simple terms: A hydroxide relaxer permanently converts part of the original cystine structure.
Japanese straightening uses reducing chemistry to temporarily disconnect some disulfide bonds, physically reshapes the hair, and then uses oxidation so bonds can form again while the hair is positioned straight.
Both create permanent texture alteration.
They're simply taking different chemical roads to get there.
Putting All Four Treatments Side by Side
Relaxer | Japanese Straightening | Keratin/Smoothing | Silk Amino Treatment | |
Main target | Cortex | Cortex | Cuticle + formula-dependent protein interactions | Primarily cuticle/damaged fiber |
Cuticle | Hair swells/becomes more permeable during processing | Becomes more permeable for chemical penetration | Surface becomes smoother/less frictional | Conditions porous/damaged areas |
Disulfide bonds | Permanently altered through lanthionization | Reduced, hair reshaped, then bonds oxidized/re-formed | Depends on specific chemistry; not classic hydroxide relaxation | Generally not permanently altered by silk amino acids themselves |
Hydrogen bonds | Affected by water/processing/styling | Strongly affected during water, drying and thermal reshaping | Heat temporarily rearranges them | May be temporarily affected during styling |
Curl change | Major/permanent | Major/permanent | Mild to significant; formula-dependent | Usually little/no permanent change from silk amino acids alone |
Frizz reduction | High | Very high | High | Mild–moderate |
Damage/porosity risk | Significant if improperly processed | Significant if improperly processed, overheated, or used on compromised hair | Depends heavily on formula, hair condition and heat | Generally lower when used as a conditioning treatment |
Wears off? | No—treated hair remains chemically altered | No—treated hair remains chemically altered | Usually diminishes gradually | Conditioning effect gradually diminishes |
New growth | Natural texture | Natural texture | Natural texture | Natural texture |
The Easiest Way to Remember the Difference
RELAXER = STRUCTURAL CHANGE THROUGH CHEMICAL CONVERSION
A hydroxide relaxer reaches the cortex and permanently chemically alters part of the structure associated with the natural curl pattern through lanthionization.
Think:
"I'm permanently chemically converting part of the structure responsible for your curl."
JAPANESE STRAIGHTENING = REDUCE → RESHAPE → RE-FORM
Japanese straightening reaches the cortex, reduces disulfide bonds, uses heat to reshape the fiber straight, and then uses oxidation to allow bonds to re-form while the hair is in that straighter configuration.
Think:
"I'm temporarily disconnecting some strong bonds, physically reshaping the hair straight, and then allowing bonds to form again in that new configuration."
KERATIN/SMOOTHING = SMOOTH + RESHAPE
Keratin/smoothing treatments primarily create smoother, shinier, less frizzy and easier-to-manage hair, while the amount and type of internal chemical interaction depend on the actual smoothing chemistry.
Think:
"I'm reducing frizz and helping the hair maintain a smoother configuration, but exactly how I'm accomplishing that depends on my formula."
SILK AMINO = CONDITION + REINFORCE
Silk amino/protein ingredients primarily help condition, smooth and temporarily reinforce porous or damaged areas.
Think:
"I'm primarily improving the condition and surface behavior of the hair unless another active straightening chemistry is included in the formula."
Why the Ingredient List Matters More Than the Marketing Name
One of the biggest misconceptions in hair education is the idea that every treatment can simply be explained as:
"We open the cuticle, put the treatment inside, and then seal the cuticle."
That's an easy explanation but scientifically, it is incomplete.
Different chemical services can cause fiber swelling, increase permeability, diffuse into different regions of the strand, deposit materials on the surface, interact with proteins, alter bonds, create crosslinks, respond to pH, and behave differently under heat.
And this becomes especially important with products marketed using terms such as:
Keratin. Silk. Amino acid. Protein. Brazilian. Smoothing. Repair. Thermal reconditioning.
Those words can tell you something about how the product is being marketed, but they don't automatically tell you which chemical reactions are responsible for the final result.
That's why understanding hair science changes the conversation.
Instead of only asking:
"What is this treatment called?"
Start asking:
What are the active ingredients? What is the pH? Is this primarily surface conditioning, or is the cortex being chemically altered? Are disulfide bonds being permanently converted, reduced and re-formed, or largely left intact? What role does heat play? And is the texture change temporary, semidurable, or permanent?
Because two clients can walk out of the salon with hair that looks equally smooth and straight—but the chemistry that created those results can be completely different.
The Bottom Line
A relaxer permanently alters the internal structure through chemical conversion associated with lanthionization.
Japanese straightening permanently alters texture through reduction, thermal reshaping, and oxidation.
A keratin/smoothing treatment creates smoother, less frizzy hair through formula-dependent surface and protein interactions, often assisted by significant heat, with results that generally diminish over time.
A straightforward silk amino treatment primarily conditions, smooths, and temporarily reinforces the fiber; silk amino acids themselves should not automatically be credited with permanent straightening.
So don't judge a professional treatment only by whether the bottle says keratin, silk, amino acid, protein, Brazilian, smoothing, thermal reconditioning, Japanese straightening, or repair.
The name is marketing. The chemistry tells you what it's actually doing to the hair.
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