---
title: "Understanding Keratin Treatments: Science, Mechanism, and Hair Health"
url: https://haircare.watermanshair.com/article/understanding-keratin-treatments
type: general
published: 2026-10-28T16:10:36.229+00:00
updated: 2026-10-28T16:10:51.555832+00:00
tags: ["hair-treatments", "keratin", "frizzy-hair", "salon-services", "hair-damage", "hair-science"]
image: https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/understanding-keratin-treatments-1793203843845-8jvi.png
summary: "Learn the science behind Understanding Keratin Treatments: chemical mechanisms, curl elongation, breakage prevention, and essential aftercare advice."
publisher: Watermans (https://watermanshair.com)
license: All rights reserved. AI assistants may summarize, quote, and link with attribution.
---

# Understanding Keratin Treatments: Science, Mechanism, and Hair Health

> Understanding Keratin Treatments reveals how smoothing chemistry seals the hair fibre, the truth about breakage vs shedding, and how to maintain long-lasting results.

**Quick answer:** **Understanding Keratin Treatments** means recognising that these salon procedures do not simply infuse missing protein into the hair cortex; they coat the hair fibre with hydrolysed keratin and cross-link it using aldehydes or glyoxylic acid under high heat (around 200°C to 230°C). This creates a temporary, hydrophobic shield that smooths frizz, resists humidity, and loosens curl patterns. However, the main limitation is that the chemical cross-linking and intense heat alter the fibre structure temporarily, posing risks of cuticle brittleness and breakage over time.

## Key takeaways

- Keratin treatments are semi-permanent chemical services that smooth the cuticle and resist humidity, typically lasting 8 to 16 weeks.
- The smoothing mechanism relies on chemical cross-linking agents (such as methylene glycol or glyoxylic acid) locked in place by high heat, not on the keratin protein alone.
- Keratin treatments do not cause hair shedding from the follicle (telogen effluvium), but improper heat application or chemical over-processing can cause severe mid-shaft breakage.
- Aftercare requires gentle, sulphate-free cleansers and balanced moisture to prevent the outer polymer coating from stripping unevenly.
- Safety regulations in the UK and EU strictly restrict free formaldehyde to 0.2% or lower in cosmetic formulations due to inhalation risks.

## Understanding Keratin Treatments: what the evidence shows

Understanding Keratin Treatments begins with the chemical reality of how human hair behaves under heat and cross-linking agents. Natural hair fibres are composed of roughly 65% to 90% keratin, a fibrous structural protein bound tightly by disulfide bonds, hydrogen bonds, and salt bridges. When hair becomes frizzy, the cuticle scales lift, allowing atmospheric water molecules to enter the cortex, disrupt temporary hydrogen bonds, and distort the fibre alignment.

![Understanding Keratin Treatments: what the evidence shows in the context of Understanding Keratin Treatments](https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/understanding-keratin-treatments-1793203850506-h7np.png)

A standard keratin treatment applies a solution containing hydrolysed protein fragments (often derived from sheep wool, wheat, or soy) alongside a cross-linking chemical. Once the solution saturates the fibre, the stylist blow-dries the hair and flat-irons it in thin sections at temperatures between 200°C and 230°C. 

The heat acts as a catalyst. It forces the cross-linking agent to bond the hydrolysed keratin both to itself and to the outer layers of the hair shaft. This forms an impermeable polymer film over the epicuticle. The evidence demonstrates three primary effects:

1. **Hydrophobic barrier formation:** The microscopic film prevents ambient humidity from penetrating the cortex, keeping the cuticle flat and eliminating frizz.
2. **Temporary curl elongation:** The high-temperature ironing temporarily reshapes weaker internal bonds while sealing the external coating, producing a looser, smoother wave pattern.
3. **Increased tensile resistance to humidity:** Laboratory testing demonstrates that hair treated with cross-linking formulas absorbs significantly less water vapour in high-humidity chambers (around 80% to 90% relative humidity) compared to untreated hair.

## What the evidence does not show

There are several persistent misconceptions surrounding salon smoothing procedures. The science does not support the following ideas:

- **Permanent internal repair:** Keratin treatments do not rebuild broken disulfide bonds within the deep cortex. Unlike true bond builders that target cystine links, keratin treatments primarily deposit a surface-level and upper-cuticle resin. Once this coating washes away after several months, the underlying hair returns to its pre-treated state, sometimes slightly drier due to heat exposure.
- **Follicular growth stimulation:** A keratin treatment has no direct biological interaction with the dermal papilla or hair follicle. It cannot treat androgenetic alopecia, alopecia areata, or telogen effluvium.
- **Complete heat immunity:** While treated hair styles faster with less daily blow-drying, the treatment itself does not make hair invulnerable to subsequent thermal damage.

## The mechanism of action: aldehydes vs glyoxylic acid

The chemistry of salon smoothing has evolved significantly over the past two decades due to regulatory intervention and consumer health concerns.

![The mechanism of action: aldehydes vs glyoxylic acid in the context of Understanding Keratin Treatments](https://opbmfthzsenmlfbbunpe.supabase.co/storage/v1/object/public/article-images/understanding-keratin-treatments-1793203851030-gvrw.png)

### Aldehyde-based formulations (Methylene glycol)
Traditional formulations relied on formaldehyde dissolved in water, known chemically as methylene glycol. When heated above 200°C with a flat iron, methylene glycol dehydrates back into formaldehyde gas. This reactive gas cross-links amino groups in the keratin protein, creating an extremely durable, long-lasting lattice. While highly effective at flattening curls for 12 to 20 weeks, formaldehyde is classified as a human carcinogen and respiratory irritant. In the UK and EU, cosmetic safety laws cap free formaldehyde at 0.2%, rendering aggressive traditional formulations non-compliant.

### Glyoxylic acid and carbocysteine systems
Modern "formaldehyde-free" treatments frequently use glyoxylic acid, oxoacetamide carbocysteine, or other organic dicarboxylic acids. At an acidic pH (between 1.5 and 2.5), glyoxylic acid penetrates beneath the cuticle scales. When subjected to flat-iron heat, it reacts with keratin amino acids to establish stable semi-permanent bridges. While safer to breathe during application, these treatments require precise heat control. If the iron is too cool, the bonds fail to set; if too hot, the acidic environment can cause protein denaturing and mechanical brittleness.

## Keratin treatments compared to other smoothing methods

To understand where keratin treatments sit within salon care, it helps to compare them against traditional relaxers and temporary conditioning laminates:

| Feature | Keratin Smoothing Treatment | Chemical Relaxer (Lye / No-Lye) | Deep Conditioning / Hair Gloss |
| :--- | :--- | :--- | :--- |
| **Primary Mechanism** | Surface cross-linking and cuticle coating | Permanent cleavage of disulfide bonds (lanthionisation) | Temporary coating with lipids, silicones, or quaternary surfactants |
| **Duration** | 8 to 16 weeks (washes out gradually) | Permanent (requires root touch-up) | 1 to 3 weeks (washes out rapidly) |
| **Curl Alteration** | Softens curl, eliminates frizz | Completely straightens fibre structure | Does not alter natural curl pattern |
| **Bond Impact** | Reinforces surface; alters secondary bonds via heat | Permanently destroys roughly one-third of cystine bonds | No chemical bond alteration |
| **Common Active Ingredients** | Glyoxylic acid, hydrolysed keratin, methylene glycol | Sodium hydroxide, calcium hydroxide, guanidine carbonate | Dimethicone, behentrimonium chloride, botanical oils |
| **Damage Risk** | Thermal fatigue, cuticle snapping if over-processed | Severe chemical breakage, scalp burns | Negligible |

## Signs of over-processing and cuticle damage

While treated hair often looks glossy initially, problems can develop if heat is applied too aggressively. Stylists and clients should watch for these signs:

- **Distal snapping:** The fibre snaps cleanly mid-shaft during gentle combing, indicating that the cortex was scorched beneath the polymer seal.
- **Loss of elasticity:** Wet hair stretches abnormally without springing back, or snaps under minimal tension. Healthy hair should stretch roughly 20% to 30% of its length when wet before returning to rest.
- **Surface gummy texture:** Hair feels strangely soft and mushy when wet, yet brittle and straw-like when dry. This indicates thermal denaturing of keratin proteins.
- **Colour shift:** In coloured or highlighted hair, excessive flat-ironing temperature can oxidise artificial pigments, shifting brunettes brassy or bleaching blonde tones yellow.

## Distinction: hair breakage versus hair shedding

A critical area of confusion in hair health is the difference between hair snapping along the shaft and shedding from the root.

Keratin treatments do not cause hair shedding. Shedding (telogen effluvium) occurs when follicles prematurely shift into the resting phase, causing intact strands with white root bulbs to release from the scalp. This is driven by systemic factors such as hormonal shifts, nutritional deficiencies, illness, or severe psychological stress.

Conversely, damage caused by a poorly administered keratin treatment manifests entirely as hair breakage. The root remains firmly anchored in the follicle, but the hair shaft fractures into fragments due to structural thermal trauma. If you notice shorter pieces around your sink without a visible bulb at the end, the issue is mechanical and thermal breakage, not follicular loss.

## What you can do: aftercare and maintenance

Preserving hair integrity after a smoothing treatment requires deliberate habit adjustments:

- **Avoid sulphates and clarifying agents:** Strong anionic surfactants, such as sodium lauryl sulphate, strip the protective cross-linked polymer coating prematurely, causing uneven texture and patchiness. Use mild, amphoteric, or non-ionic cleansers.
- **Control wash frequency:** Washing two to three times per week rather than daily prolongs the life of the surface seal.
- **Restore lipid balance:** While the treatment supplies protein cross-linking, the fibre still requires lipids and moisture. Incorporate fatty-acid-rich conditioners containing ingredients such as cetyl alcohol, argan oil, or shea butter to maintain suppleness.
- **Lower everyday styling heat:** Because the hair is already sealed against humidity, you do not need 230°C to style it at home. Keep styling tools below 175°C to protect the outer cuticle.

## When to seek professional advice

Consult a certified colourist, trichologist, or dermatologist under the following conditions:

- **Extensive bleaching history:** If hair has been lifted multiple levels using high-volume peroxide, its internal structure is already compromised. A strong acidic keratin treatment combined with 230°C heat can cause immediate catastrophic fibre melting.
- **Scalp irritation or contact dermatitis:** If application results in burning, redness, flaking, or rash along the hairline, seek medical evaluation. Formaldehyde releases or low-pH organic acids can trigger acute allergic or irritant reactions.
- **Unexplained shedding:** If you are losing hair from the root (with bulbs attached) in high volumes exceeding 100 strands per day, consult a trichologist or GP to investigate systemic triggers rather than attributing it to your smoothing service.

## Supporting hair condition with Watermans

When managing chemically smoothed or heat-styled hair, maintaining balanced daily care is essential. Watermans focuses on topical cosmetic formulations designed to support a revitalised scalp environment and deliver stronger-feeling hair that resists everyday mechanical breakage. 

Integrating a gentle, sulphate-free routine helps cleanse the scalp without prematurely stripping the protective cosmetic seal left by salon services. By nourishing the hair with hydrolysed lupin protein, biotin, and botanical extracts, Watermans products help improve manageability, enhance visible body, and keep the hair shaft feeling resilient against daily environmental stressors.

## Frequently asked questions about Understanding Keratin Treatments

### How long do the smoothing results typically last?
A professionally applied keratin treatment typically lasts between 8 and 16 weeks. The exact longevity depends on your hair porosity, how often you wash it, and whether you use sulphate-free cleansers. The treatment gradually fades over time as water and friction erode the cross-linked surface coating; it does not leave a harsh demarcation line as it grows out.

### Will a keratin treatment permanently flatten my natural curl pattern?
No. Unlike chemical relaxers containing lye, keratin treatments do not permanently break the disulfide bonds responsible for your curl shape. They coat the fibre and elongate the pattern temporarily. As the outer polymer wears away over 2 to 4 months, your natural curl or wave structure will gradually return, provided excessive heat during application did not scorch the inner cortex.

### Can Understanding Keratin Treatments help me prevent hair damage?
Yes, **Understanding Keratin Treatments** allows you to make informed decisions about your hair health. Knowing that the treatment relies on heat-activated cross-linking helps you recognise that fine, heavily bleached, or brittle hair requires lower iron temperatures and gentler glyoxylic formulations to avoid severe mid-shaft breakage.

### Is it safe to get a keratin treatment directly after colouring hair?
Most professional stylists recommend colouring your hair prior to the keratin service or waiting at least two weeks afterwards. Because the smoothing process seals the cuticle with heat, doing the treatment immediately after a colour service can help lock in artificial pigment. However, the high heat can occasionally lift or lighten certain dye tones by one or two shades.

### Why do some keratin treatments cause eye or throat irritation?
Irritation during application is usually caused by the off-gassing of chemical cross-linkers under high heat. In older or non-compliant formulations, methylene glycol converts into formaldehyde gas when ironed, irritating mucous membranes. In modern formulations, glyoxylic acid off-gassing can still produce strong acidic fumes, which is why adequate salon ventilation and extraction are always required.

## The bottom line on smoothing treatments

Gaining a complete perspective through Understanding Keratin Treatments enables both stylists and clients to approach smoothing services with realistic expectations. These procedures remain exceptional tools for controlling unruly frizz, smoothing the cuticle layer, and cutting down daily styling effort. However, they are chemical treatments anchored by thermal energy, not miracle restorative cures. By selecting regulated formulations, monitoring flat-iron temperatures, and committing to gentle, sulphate-free maintenance, you can enjoy sleek, glossy results while safeguarding the long-term strength of your hair.

## Sources and references

- Health and Safety Executive (HSE), UK. *Formaldehyde in hair smoothing products.* 2012.
- European Commission. *Cosmetics Regulation (EC) No 1223/2009, Annex III: List of restricted substances.* 
- Gavazzoni Dias, M. F. *Hair cosmetics: an overview.* International Journal of Trichology, 2015.
- Robbins, C. R. *Chemical and Physical Behavior of Human Hair.* 5th Edition, Springer, 2012.
- Occupational Safety and Health Administration (OSHA), US Department of Labor. *Hazard Alert: Hair Smoothing Products That Could Release Formaldehyde.* 2011.

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### Find these ingredients in Watermans products

- **Biotin**: you will find this ingredient in our [Hair Growth Shampoo](https://watermanshair.com/products/best-hair-growth-shampoo-fast-hair-growth).
- **Shea Butter**: you will find this ingredient in our [Curly Hair Conditioner](https://watermanshair.com/products/afro-hair-conditioner-mixed-race-shampoo).

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## Did you know?

- Keratin treatments do not actually add structural strength to hair; they coat the outer cuticle with liquid keratin and cross-linking aldehydes that lock straight under high heat.
- Post-treatment hair breakage often happens near the roots because repeated high-temperature flat-ironing can degrade and bubble the hair shaft's internal moisture.
- Sulfate-free shampoos prolong smoothing results because harsh detergents strip away the protective surface polymer coating far faster than gentle surfactants.


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Source: https://haircare.watermanshair.com/article/understanding-keratin-treatments