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A keratin treatment is a cosmetic or beauty product used to straighten hair. It is also called a Brazilian keratin treatment or a “Brazilian blowout.”

Advertising for keratin treatment hair products claims that it will make naturally curly or wavy hair straighter and smoother. The products are also said to remove hair frizz, improve color and shine, and make hair look healthier.

This treatment can also come with some unwanted side effects, and could present some safety issues.

Keratin is a natural type of protein in your skin, hair, and nails. This protein forms fibers that make it strong.

Keratin used in beauty treatments is usually from these animal parts. While it is a natural protein, these products are made with several other added ingredients. Keratin treatments typically contain a chemical called formaldehyde.

The American Cancer Society warns that formaldehyde is a known carcinogen. This means that it may cause cancer or help cancer to grow. Products with this chemical release formaldehyde gas into the air. Formaldehyde may also trigger other health side effects.

Side effects from keratin treatments are not widely reported. It is not yet known how often negative effects happen. Additionally, the long-term effects of this hair treatment have not been tested.

The lasting health effects of keratin products on people who are hairdressers and people who get this treatment are not known. It’s important to know the possible side effects and risks of a keratin treatment. This may help you decide if this beauty product is right for you.

People who use keratin treatments on their hair report some benefits. Results depend on your hair type and texture. They also vary depending on how healthy your hair is to begin with and how thick it is. Different types of keratin treatments may give varying results.

Keratin treatments work by:

  • smoothing down your hair
  • filling in gaps in the proteins of each hair strand
  • helping hair look thicker and smooth
  • making hair look glossy and straighter in appearance
  • making your hair more manageable

Formaldehyde is a strong-smelling, colorless gas. You may have smelled it if you have ever been near embalming fluid that is used in laboratories and funeral homes. Much smaller amounts are used in products.

A 2012 study of keratin brands marketed in South Africa found that 6 out of 7 products contained 0.96 percent to 1.4 percent formaldehyde levels. This is five times higher than the recommended safe level of 0.2 percent.

Formaldehyde gas is released into the air when these products are used. You may breathe in the fumes. Your body may absorb it through the skin. It may also be given off later as the product breaks down.

Some people are more sensitive to this chemical. Formaldehyde may increase the risk of some cancers over time. A medical review notes it’s been linked to a higher risk of cancers of the nose and the blood cancer leukemia. Formaldehyde may also trigger other health effects, like:

  • stinging, itching burning eyes
  • nose and throat irritation
  • runny nose
  • allergic reactions
  • coughing
  • wheezing
  • chest tightness
  • itchy skin
  • skin rash
  • scalp irritation
  • scalp burns or blisters
  • headaches
  • nausea
  • mood changes
  • hair breakage or damage
  • hair loss

Formaldehyde is also found in some beauty, industrial, and home products, such as:

  • nail polish
  • nail glue and remover
  • hair glue
  • hair dyes
  • hair shampoos
  • home furnishings
  • plastics
  • paints
  • cleaning products
  • textiles
  • pesticides

Five of the brands that tested positive for formaldehyde in the study mentioned above, were labeled as formaldehyde-free. This shows that manufacturers may not be accurate in labeling products.

Some companies also list formaldehyde with other names. Formaldehyde may be listed as:

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

Your keratin treatment may not even have to contain formaldehyde to release it into the air. The American Cancer Society notes that some chemicals that are used to help keep products from spoiling give off formaldehyde. These include:

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

Keratin treatments can help improve the look and feel of your hair. Other more natural treatments can also help make your hair more smooth and silky in appearance.

Using a flat iron straightens hair by temporarily smoothing the fibers in the strands. You can get a similar effect by blow-drying hair with a large, round bristle brush.

Curly and wavy hair is normally drier than other hair types. Avoid washing hair more than once every two days. Too much shampoo can remove natural hair oils.

Moisturize hair regularly to help make dry hair smoother, shinier and stronger. Natural moisturizing products can help keep your hair and scalp healthy. Try products like:

Look for products with natural moisturizers online here.

Keratin hair treatments may sound like a quick fix for curly or wavy hair, but it may cost you more in the long term. Tests show that keratin treatments contain unsafe levels of formaldehyde and other chemicals.

Formaldehyde is a known cancer-causing chemical. It can also cause skin reactions and other side effects. Hair and beauty professionals are exposed to formaldehyde and other chemicals regularly. This may also lead to health effects.

Ask your hairdresser what kind of keratin treatment they use before you book your hair appointment. Check the labels carefully. Ask for other safer or natural alternatives to straighten hair.

It is especially important to avoid formaldehyde and other harmful chemicals if you are pregnant or breastfeeding. Avoid bringing children to beauty salons where they may be exposed to chemicals in the air.

If you have asthma, allergies, or are sensitive to smells, you may also be at higher risk of side effects from chemicals in the air.