What Are the Side Effects of a Keratin Treatment?

Keratin treatments are used to smooth and often straighten hair. Yet this cosmetic procedure can carry side effects and potential health concerns.

A keratin treatment — sometimes called a Brazilian keratin treatment or Brazilian blowout — involves applying product to the hair, blow-drying, and sealing the strands with a flat iron. The goal is to smooth the hair cuticle, reduce frizz, and sometimes relax curls or waves.

Keratin itself is a naturally occurring protein found in skin, hair, and nails. A keratin treatment deposits extra keratin onto the hair, which can help reduce frizz, boost shine, and strengthen the hair shaft. For people with curly or wavy hair, these treatments can also create a straighter appearance.

However, keratin treatments can produce undesirable side effects and may pose safety concerns.

Possible side effects

The keratin used in salon products is typically derived from human or animal hair, skin, or nails. Although keratin is a natural protein, commercial preparations include several additional ingredients, often including formaldehyde or formaldehyde-releasing compounds.

Health authorities warn that formaldehyde is a recognized carcinogen. That means it may cause cancer or encourage the growth of cancerous cells. Formaldehyde can also provoke other adverse health reactions.

Regulators note that formaldehyde and related chemicals in keratin products can lead to:

• eye irritation
• headaches
• dizziness
• sore throat
• cough
• wheezing
• nausea
• chest discomfort
• vomiting
• skin rash

Both clients who have received keratin treatments and stylists who perform them have reported these symptoms.

These reactions generally occur during or shortly after treatments that contain formaldehyde. It remains uncertain whether exposure from keratin treatments leads to long-term health consequences, and if so, what those outcomes might be.

Benefits

The advantages you experience from a keratin treatment depend on your hair type and the specific formula used.

Typically, a keratin treatment may offer the following benefits:

• Smoother, silkier hair. Sun exposure, hair dye, and various chemical procedures can strip hair of natural keratin, leaving porous, weaker areas prone to breakage. Keratin treatments help “refill” these depleted spots, resulting in a smoother hair shaft and a shinier, silkier appearance.
• Straighter hair. Depending on the product used, keratin treatments can relax curls and waves to create a straighter look.
• Tamed curls. Not all keratin treatments produce poker-straight hair. Some formulations primarily reduce frizz, leaving curls or waves softer and more defined.
• Stronger strands. By restoring lost keratin within the hair shaft, treatments can make hair more resilient and less likely to break, which for some people enables longer growth.
• Fuller-looking hair. Replenishing keratin can also give the impression of thicker hair in addition to improving strength.

If you opt for a keratin service, discuss your goals with your stylist. They can select products and a technique aligned with the outcome you want.

How significant is the formaldehyde risk?

One problem with formaldehyde in keratin products is that actual levels may be higher than what’s listed on the label.

For instance, a 2014 study of keratin brands sold in South Africa reported that six of seven products contained between 0.96 percent and 1.4 percent formaldehyde — up to five times the suggested safety threshold of 0.2 percent.

An earlier 2011 study similarly detected higher-than-declared formaldehyde in four different keratin brands.

Remember that keratin treatments are usually performed in salons where multiple clients may be treated throughout the day, potentially raising airborne exposure levels for workers and other patrons.

The Agency for Toxic Substances and Disease Registry reports that formaldehyde concentrations of 0.1 to 0.5 parts per million (ppm) can cause nasal and eye irritation, neurological symptoms, and increase the risk of asthma and allergic reactions. At 0.6 to 1.9 ppm, people may develop eczema or altered lung function.

The 2011 study cited above measured formaldehyde levels in salons during keratin services. During blow-drying, concentrations ranged from 0.08 to 3.47 ppm; during flat-ironing, they ranged from 0.08 to 1.05 ppm. The higher values in both sets far exceed levels that many people can tolerate.

If you receive a single treatment, you might not notice significant effects. But for stylists and salon workers who are repeatedly exposed, these concentrations could pose a meaningful health risk over time.

Are formaldehyde-free options safe?

Manufacturers have introduced so-called formaldehyde-free keratin products, but labeling can be misleading. In the studies mentioned earlier, several products that tested positive for formaldehyde were marketed as formaldehyde-free.

Sometimes a product lists formaldehyde under alternate names, such as:

• aldehyde
• bonded aldehyde
• formalin
• formic aldehyde
• methanediol
• methanal
• methyl aldehyde
• methylene glycol
• methylene oxide
• morbicid acid

Other times, ingredients that release formaldehyde as a preservative may be present, like:

• benzylhemiformal
• diazolidinyl urea
• imidazolidinyl urea
• quaternium-15

Formaldehyde contributes to the effectiveness of many keratin treatments. Because of that, truly formaldehyde-free products that perform the same way can be hard to find. If you’re thinking about a keratin procedure, research different brands and check ingredient lists. Consulting a stylist experienced with keratin treatments can also help you identify safer choices and they may offer a pre-treatment consultation.

Alternatives

If you’re uneasy about formaldehyde exposure, there are other methods to achieve similar results to keratin treatments.

Heat styling with a blow-dryer or flat iron can temporarily smooth hair.

Maintaining hair health through proper moisturizing — especially if you regularly use heat tools — helps preserve smoothness and shine.

Washing hair less frequently can retain natural oils; some people try the “no poo” approach to reduce stripping natural moisture.

Using products with natural emollients can also help, such as:

• olive oil
• argan oil
• coconut oil
• shea butter
• sunflower oil

For additional pointers, see guides on achieving glossy, healthy hair.

The takeaway

Keratin treatments can deliver smoother, shinier hair, but they commonly involve formaldehyde or related compounds, which can cause a variety of side effects.

Although some products claim to be formaldehyde-free, many still contain forms of formaldehyde or agents that release it.

It’s not clear whether an occasional keratin treatment leads to long-term health problems. If you have heightened sensitivity, asthma, or allergies, you may want to avoid these procedures.

Keratin treatments are also best avoided during pregnancy and while breastfeeding.