Keratin is the protein your hair is actually made of, so a keratin treatment sounds like it should be one of the safest things you can do. The problem is that the phrase covers two very different things, and one of them has a formaldehyde problem serious enough that the FDA has moved to ban it. Here is the distinction that matters, and how to get keratin's benefits safely.
Two Very Different Things Called Keratin
A salon keratin treatment, often known as a Brazilian blowout, is a topical smoothing service. The formula is applied to the hair and sealed in with a flat iron to relax curl and frizz for weeks at a time. Oral keratin, by contrast, is a supplement ingredient you take internally to support the hair from within. They share a name and almost nothing else, and nearly all the side-effect concern belongs to the first one.
The Side Effects of Salon Keratin Treatments
Many salon smoothing treatments rely on formaldehyde, or ingredients that release it, because formaldehyde is what locks the hair into its smoothed shape. When heat is applied, that formaldehyde is released as a gas, and it can cause burning and watering eyes, an irritated nose and throat, coughing, and skin irritation for both the client and the stylist.
The concern goes beyond irritation. In 2022, a study from the National Institutes of Health linked frequent use of hair-straightening products to a higher risk of uterine cancer. In October 2023 the FDA proposed a rule to ban formaldehyde and formaldehyde-releasing chemicals in hair-smoothing and straightening products, and California banned formaldehyde in personal-care products starting in 2025. Compounding the problem, investigators have found that some products labeled formaldehyde-free actually contained it when tested.
Who Should Be Cautious
Pregnant women, salon professionals with repeated exposure, and anyone with asthma or respiratory sensitivity have the strongest reasons to avoid formaldehyde-based smoothing. If you do get a treatment, insist on a genuinely formaldehyde-free method and good ventilation, and be skeptical of the label.
The Other Keratin: A Safer Way to Get the Benefits
Here is the good news the scare stories skip: the keratin your hair benefits from does not have to come from a formaldehyde-sealed salon service. Cynatine HNS is a solubilized keratin taken as a supplement. It supports hair strength and thickness from the inside, with no formaldehyde and no fumes, and it is the hero ingredient in the HAIRLOVE Growth Complex. If you want to understand how it works, our deep dive on Cynatine HNS and our clinical studies page cover the detail. It is a different route to keratin's benefits, and a far cleaner one.
Reading Between the Lines
The side effects people mean when they search keratin treatment side effects are really formaldehyde side effects, from salon smoothing services, not from keratin itself. Keratin the protein is not the problem. If you want its benefits without the formaldehyde risk, taking it internally is the safer path, and if you do want a salon smoothing service, demand a formaldehyde-free one.
