Are keratin hair treatments safe during pregnancy?

The verdict

No. Of everything in this batch, this is the treatment with the clearest case for postponing, and the reason has nothing to do with keratin.

The FDA states that hair smoothing products often contain formaldehyde, also known as formalin and methylene glycol, and that when the solution is heated, the formaldehyde is released into the air as a gas. It adds that if the salon is not properly ventilated, both the salon professionals and their clients are at risk of inhaling the released formaldehyde.

Formaldehyde has been classified as a human carcinogen by the International Agency for Research on Cancer. Independently of that, the FDA notes that at airborne levels above 0.1 parts per million some people experience watery eyes, burning sensations in the eyes, nose and throat, coughing, wheezing, nausea and skin irritation.

You are lying in a chair, under heat, for two to three hours, breathing the air directly above your own head. There is no version of this where the exposure is trivial.

How the treatment works, and why heat is the problem

A Brazilian blowout, keratin treatment or hair smoothing service applies a solution to the hair and then seals it in with heat, usually a blow dry followed by repeated passes with straightening irons at high temperature. The FDA describes exactly this sequence: a straightening or smoothing solution applied to the hair, followed by a heat treatment that seals the solution in.

The formaldehyde is not free in the bottle in a form you would smell on opening it. Methylene glycol, its dissolved form, converts and releases formaldehyde gas when heated. That is why the ironing stage is where the airborne concentration spikes, and why a product that looks innocuous on the shelf becomes an inhalation exposure in the chair.

The FDA is explicit that greater exposure, in both duration and concentration, means higher potential health risks, and lists the reactions that have been reported: eye problems or irritation, nervous system problems such as headaches and dizziness, respiratory tract problems including sore throat, cough and wheezing, nausea, chest pain, vomiting and rash.

Reading the label

The FDA's advice for consumers is to look for three names on the ingredient list: formaldehyde, formalin and methylene glycol. It also warns about a gap in labelling: products marketed only to salon professionals are not required to carry a consumer ingredient list under the Fair Packaging and Labeling Act, because that law applies to products sold retail. Professional products must carry directions for safe use and warnings, and OSHA requires a Safety Data Sheet for products containing hazardous chemicals.

The FDA's practical instruction is to ask your salon professional whether a product contains formaldehyde-related ingredients, and that if they are unsure, you may not want to use the product. It also notes, from its own focus group research, that salon customers were less knowledgeable about the risks than stylists, with some reporting they received no information before treatment and others reporting side effects during it.

Treat "formaldehyde-free" claims with caution. Products have been marketed that way while still releasing formaldehyde on heating; the FDA has issued warning letters to two companies citing both safety and labelling violations, noting that labelling failures included failure to warn consumers of potential health risks.

Why pregnancy tightens the case

There is no study of keratin treatments in pregnancy, and it would be wrong to claim otherwise. What tightens the case is a set of ordinary considerations stacking in the same direction.

The exposure is inhalational and sustained, in a room chosen by someone else, at a concentration you cannot measure. The benefit is entirely cosmetic and entirely deferrable. Nausea and heightened smell sensitivity in the first trimester make an irritant gas particularly unpleasant. And the treatment is a repeat service, so declining it is postponing rather than abandoning it.

There is also a hair-specific reason to wait that has nothing to do with chemistry. Hair behaves differently in pregnancy and again in the months after birth, when the postpartum shedding phase changes both texture and volume. A chemical straightening service applied to pregnancy hair may not deliver the result you paid for once that settles.

What is safe instead

Heat styling with straighteners or a blow dry involves no chemistry at all and is not restricted. Mechanical methods, blow-dry brushes and smoothing serums that do not require a heat-set chemical reaction sit in the same category.

If you work in a salon, this is a different and more serious question than an occasional client visit. OSHA has issued a hazard alert to salon owners and workers about formaldehyde exposure from hair smoothing products and set a formaldehyde standard, 29 CFR 1910.1048, limiting allowable airborne levels. That standard applies to all employers using formaldehyde or products that release it. A pregnant stylist performing these services repeatedly should be raising it with her employer as a workplace risk assessment, not treating it as a personal choice.

Where guidance genuinely differs

The UK and EU force the label; the US regulates the air. The Cosmetic Products Regulation, which applies in Ireland and across the EU and was carried into UK law after Brexit, requires that all finished products containing formaldehyde, or containing substances that release it, be labelled with the warning "contains formaldehyde" where the concentration in the finished product exceeds 0.05 per cent. The United States imposes no equivalent consumer warning; the FDA does not approve cosmetics, and companies are responsible for the safety and labelling of their own products. The American controls that do exist are occupational, through OSHA's formaldehyde standard and hazard alert, and they protect the workplace rather than informing the client.

That difference is smaller in practice than it looks. A labelling requirement does not reach a product imported directly, bought online or used in a salon from a professional-only container, and the FDA's own warning letters show that mislabelling has been a recurring problem. The consumer instruction is therefore the same in both countries: ask what is in it, and if nobody can tell you, do not have it.

No health body has published pregnancy-specific advice on this. Neither the NHS, ACOG, the CDC nor the FDA addresses keratin treatments in pregnancy directly. The verdict above is assembled from the FDA's consumer guidance on the product, IARC's classification of the chemical and OSHA's workplace standard, not from an obstetric recommendation, and it is fair to say so.