Hair straighteners

Some smoothing products, especially keratin smoothing or Brazilian smoothing, contain formaldehyde or glutaraldehyde, or formaldehyde releasers such as methylene glycol or glyoxylic acid (Gavazzoni 2015). The concentration of formaldehyde in these products should not exceed 2% ^{(Maneli 2014, Monakhova 2013)}

Its use increases the concentration of formaldehyde in the air of hairdressing salons well above the maximum safety level of 0.1 ppm. ^{(Pexe 2019, Monakhova 2013, Pierce 2011)}

Formaldehyde and glutaraldehyde have mutagenic capacity, are carcinogenic ^{(White 2021, Peteffi 2016, Gavazzoni 2015, Mazzei 2010)}, can damage the kidneys ^{(Mitler 2021, Ahmed 2019)} or cause asthma ^{(Dahlgren 2018)}. Their use has been limited in many countries.

Other smoothing products, such as sodium hydroxide, lithium hydroxide, calcium hydroxide or ammonium thioglycolate, used in so-called Japanese smoothing, or acetic acid, decylene glycol and caprylyl glycol  are not mutagenic and are considered safe ^{(Gavazzoni 2015)}. These products may also contain chemicals that cause contact dermatitis. ^{(Thomas 2021, Van Lerberghe 2014)}

An increased risk (OR 2.43) was observed between maternal exposure to hair straightening products during lactation and acute myeloid leukemia in infants. ^{(Couto 2013)}

An increased risk (OR 1.78) was observed between maternal exposure to hair straightening products in the first trimester of pregnancy and childhood acute lymphocytic leukemia. ^{(Couto 2013)}

It is recommended to limit its use, avoid products containing formaldehyde or that release formaldehyde, frequently labelled as “without formaldehyde” ^{(Gavazzoni 2015, Weathersby 2013)}, comply with the safety standards of use that come in the containers, keep the chest area clean and wear short or gathered hair in order to avoid the absorption of potentially toxic compounds by the infant.

Hairdressing workers are more exposed ^{(Pexe 2019, Aglan 2018, Galiotte 2008)} and must strictly comply with safety standards (use of gloves, ventilation of the premises and time limitation, among others) and use legally authorized products.

See below the information of this related product:

• Formaldehyde (Unsafe. Moderate/severe adverse effects. Compatible under certain circumstances. Follow-up recommended. Use safer alternative or discontinue breastfeeding from 5 to 7 T ½ . Read Commentary.)