Honest answers. No sugarcoating.
Keratin treatment side effects.
Keratin treatments have real benefits — but some have real risks too. The side effects people worry about are almost all caused by formaldehyde-based treatments. Here is what you actually need to know, and how to avoid the dangers entirely.
The real risks
Side effects of formaldehyde-based keratin treatments.
Most of the side effects associated with keratin treatments come from one ingredient: formaldehyde. Many traditional keratin treatments contain formaldehyde or methylene glycol, which releases formaldehyde gas when heated with a flat iron during application.
Formaldehyde is classified as a known human carcinogen by the International Agency for Research on Cancer (IARC). During a formaldehyde-based keratin treatment, both the client and the stylist are exposed to toxic fumes that can cause burning eyes, sore throat, coughing, headaches, and respiratory irritation.
Salon workers who apply these treatments regularly face the greatest risk. Studies have documented formaldehyde levels in salons during keratin treatments that far exceed occupational safety limits — even with ventilation.
Beyond the health risks, formaldehyde-based treatments often require very high flat iron temperatures (230°C and above) to activate the formula. This extreme heat, combined with the chemical process, can cause genuine hair damage — dryness, brittleness, and breakage, especially on fine, bleached, or already-compromised hair.
Respiratory irritation
Burning eyes, sore throat, coughing during and after application
Formaldehyde exposure
A known carcinogen — cumulative risk with repeated exposure
Thermal hair damage
Extreme flat iron heat can cause breakage and protein loss
Allergic reactions
Scalp irritation, redness, and contact dermatitis in some people
The safe alternative
Formaldehyde-free treatments eliminate the main risks.
The side effects people fear most — toxic fumes, carcinogen exposure, respiratory damage — are all caused by formaldehyde. Remove the formaldehyde, and you remove the danger.
QIQI Hair Controller uses a cysteine-based formula that restructures hair bonds without any formaldehyde or aldehyde derivatives. No toxic fumes are released during application. It is safe to use at home in a normal bathroom without commercial ventilation.
Nanokeratin System uses a nano-molecular keratin infusion that coats and smooths the hair without formaldehyde. All seven specialist formulas are verified free of formaldehyde and aldehydes.
Both treatments work at lower processing temperatures than traditional formaldehyde-based products, which means less thermal stress on your hair. When paired with proper sulfate-free aftercare, they actually improve hair condition over time rather than degrading it.
Formaldehyde
Zero
Toxic fumes
None
Carcinogen risk
Eliminated
Safe at home
Yes
Worth knowing
Mild effects you might notice — even with safe treatments.
Even formaldehyde-free keratin treatments involve a chemical process, and it is honest to say there can be some mild, temporary effects. None of these are dangerous, but they are worth knowing about:
Temporary dryness
Some people notice their hair feels slightly dry or stiff for the first 2–3 days after treatment. This settles once you wash and condition. Using the recommended sulfate-free aftercare from day one helps significantly.
Curl pattern change
Keratin treatments are designed to relax curl. If you have natural curls and want to keep some texture, choose a lighter formula or discuss your goals before application. With QIQI, you can control the level of straightening vs smoothing based on your flat iron technique.
Sulfate-free aftercare required
After any keratin treatment, you need to switch to sulfate-free shampoo and conditioner. Sulfates strip the keratin coating and shorten your results. This is not a side effect as such, but it is a real lifestyle change worth noting.
Initial scent during application
Some formaldehyde-free treatments have a mild scent during the flat ironing stage. This is not toxic fumes — it is the product being sealed into the hair. It dissipates quickly and is nothing like the strong chemical smell of formaldehyde treatments.
Recommended safe treatments
Formaldehyde-free keratin treatments we sell.
Every treatment we stock is 100% formaldehyde-free and aldehyde-free. No exceptions. We chose QIQI and Nanokeratin specifically because they deliver professional results without any of the health risks.
QIQI Hair Controller — Permanent smoothing, up to 5 months
From £119 · 150g
Hair Controller — Thick & Coarse
Formaldehyde-free permanent smoothing treatment for thick, coarse, and afro-textured hair. Softens disulfide bonds under heat for lasting frizz control — from defined curls to fully straight. QIQI Hair Controller results last up to 5 months.
Shop now →
From £119 · 150g
Hair Controller — Wavy & Curly
Permanently reduces frizz and enhances natural pattern definition — or delivers a smooth, controlled finish. Designed specifically for wavy and curly hair. Formaldehyde-free. Lasts up to 5 months.
Shop now →
From £119 · 150g
Hair Controller — Thin & Delicate
Formaldehyde-free permanent smoothing for fine, colour-treated, or delicate hair. Eliminates frizz and reduces volume without over-processing. QIQI Hair Controller safe for bleached and highlighted hair. Results last up to 5 months.
Shop now →Nanokeratin System — Temporary smoothing, 12–16 weeks
Refortify Smoother — Afro & Textured Hair
From £279
Revive Smoother — Natural Hair
From £279
Refine Smoother — Colour-Treated Hair
From £279
Replenish Smoother — Blonde & Bleached Hair
From £279
Resmooth Hair Smoother
From £129
Retexture Hair Smoother
From £129
Rexten Hair Safeguard — Extensions
From £139
Read our full guide to formaldehyde-free keratin treatments →
Common questions
Keratin treatment side effects — FAQ
What are the side effects of keratin treatment?
Side effects depend entirely on the type of treatment. Traditional keratin treatments containing formaldehyde can cause respiratory irritation, burning eyes, throat irritation, headaches, and in some cases allergic reactions. The formaldehyde released during heat application is classified as a known carcinogen. Formaldehyde-free treatments like QIQI Hair Controller and Nanokeratin System eliminate these health risks. Possible mild effects with any keratin treatment include temporary hair dryness in the first few days, a slight change in curl pattern, and the need to switch to sulfate-free shampoo.
Does keratin treatment cause hair loss?
Keratin treatment itself does not cause hair loss. However, formaldehyde-based treatments combined with excessive flat iron heat during application can weaken the hair shaft, leading to breakage — which is sometimes mistaken for hair loss. The high temperatures required to seal in formaldehyde-based formulas (often 230°C+) can cause thermal damage, especially on fine or already-damaged hair. Formaldehyde-free treatments use lower processing temperatures and gentler bonding agents, significantly reducing the risk of breakage.
Is keratin treatment safe during pregnancy?
Formaldehyde-based keratin treatments are not recommended during pregnancy due to the inhalation of formaldehyde fumes, which is a known carcinogen and respiratory hazard. For formaldehyde-free treatments, there are no specific clinical studies on their use during pregnancy. Most dermatologists and obstetricians advise avoiding chemical hair treatments during pregnancy as a general precaution. We are not medical professionals and cannot give medical advice — speak to your doctor or midwife before using any chemical hair treatment while pregnant or breastfeeding.
Can keratin treatment damage your hair?
Traditional formaldehyde-based treatments can damage hair because the application process requires very high flat iron temperatures to activate the formaldehyde, which can cause thermal stress and protein loss. Over time, repeated applications can leave hair feeling dry and brittle. Formaldehyde-free treatments work through different mechanisms — QIQI uses cysteine-based bonding and Nanokeratin uses a nano-molecular keratin infusion — both of which are gentler on the hair structure. When used with proper aftercare, they actually improve hair condition over time.
What happens when keratin treatment wears off?
When a keratin treatment wears off, your hair gradually returns to its natural texture. It does not fall out or become damaged from the treatment fading. With QIQI Hair Controller, results last up to 5 months and the treated portion of hair remains smooth — new growth comes in at your natural texture. With Nanokeratin System, the smoothing effect gradually fades over 12–16 weeks as the keratin coating naturally washes away. Your hair will not be worse than it was before treatment.
Are there long-term effects of keratin treatments?
Long-term effects depend on the product used. Repeated exposure to formaldehyde-based treatments carries cumulative health risks — studies have linked chronic formaldehyde exposure to respiratory disease and increased cancer risk among salon workers. For formaldehyde-free treatments, there are no known long-term negative effects. Many people use QIQI and Nanokeratin treatments repeatedly over years with no adverse effects. If anything, the keratin and conditioning agents in formaldehyde-free formulas tend to improve hair condition with continued use.
Free UK delivery over £80
Skip the side effects. Keep the results.
Every treatment we sell is formaldehyde-free and aldehyde-free. Professional smoothing without the health risks. Dispatched within 1–2 working days.