Last update March 31, 2023

Hair straighteners

Limited compatibility

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.

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 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.

Suggestions made at e-lactancia are done by APILAM team of health professionals, and are based on updated scientific publications. It is not intended to replace the relationship you have with your doctor but to compound it. The pharmaceutical industry contraindicates breastfeeding, mistakenly and without scientific reasons, in most of the drug data sheets.

Jose Maria Paricio, Founder & President of APILAM/e-Lactancia

Your contribution is essential for this service to continue to exist. We need the generosity of people like you who believe in the benefits of breastfeeding.

Thank you for helping to protect and promote breastfeeding.

José María Paricio, founder of e-lactancia.


Hair straighteners belongs to this group or family:


  1. White AJ, Gregoire AM, Taylor KW, Eberle C, Gaston S, O'Brien KM, Jackson CL, Sandler DP. Adolescent use of hair dyes, straighteners and perms in relation to breast cancer risk. Int J Cancer. 2021 May 1;148(9):2255-2263. Abstract
  2. ABA - Australian Breastfeeding Association. Beauty treatments and breastfeeding. None 2021 Full text (link to original source) Full text (in our servers)
  3. Thomas ZM, Jamiolkowski D, Chantraine S, Steveling-Klein E, Hofmeier KS, Hartmann K. Contact dermatitis to hair cosmetics: Current diagnostic recommendations. J Dtsch Dermatol Ges. 2021 Aug 24. Abstract
  4. White AJ, Sandler DP, Gaston SA, Jackson CL, M O'Brien K. Use of hair products in relation to ovarian cancer risk. Carcinogenesis. 2021 Jun 26. pii: bgab056. Abstract
  5. Mitler A, Houri S, Shriber L, Dalal I, Kaidar-Ronat M. Recent use of formaldehyde-'free' hair straightening product and severe acute kidney injury. Clin Kidney J. 2021 Jan 11;14(5):1469-1471. Abstract
  6. Aglan MA, Mansour GN. Hair straightening products and the risk of occupational formaldehyde exposure in hairstylists. Drug Chem Toxicol. 2020 Sep;43(5):488-495. Abstract
  7. Eberle CE, Sandler DP, Taylor KW, White AJ. Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women. Int J Cancer. 2020 Jul 15;147(2):383-391. Abstract
  8. Pexe ME, Marcante A, Luz MS, Fernandes PHM, Neto FC, Sato APS, Olympio KPK. Hairdressers are exposed to high concentrations of formaldehyde during the hair straightening procedure. Environ Sci Pollut Res Int. 2019 Sep;26(26):27319-27329. Abstract
  9. Ahmed HM, Rashad SH, Ismail W. Acute Kidney Injury Following Usage of Formaldehyde-Free Hair Straightening Products. Iran J Kidney Dis. 2019 Mar;13(2):129-131. Abstract
  10. Dahlgren JG, Talbott PJ. Asthma from hair straightening treatment containing formaldehyde: Two cases and a review of the literature. Toxicol Ind Health. 2018 Apr;34(4):262-269. Abstract
  11. Peteffi GP, Antunes MV, Carrer C, Valandro ET, Santos S, Glaeser J, Mattos L, da Silva LB, Linden R. Environmental and biological monitoring of occupational formaldehyde exposure resulting from the use of products for hair straightening. Environ Sci Pollut Res Int. 2016 Abstract
  12. Gavazzoni Dias MF. Hair cosmetics: an overview. Int J Trichology. 2015 Abstract Full text (link to original source) Full text (in our servers)
  13. Van Lerberghe L, Baeck M. A case of acute contact dermatitis induced by formaldehyde in hair-straightening products. Contact Dermatitis. 2014 Abstract
  14. Maneli MH, Smith P, Khumalo NP. Elevated formaldehyde concentration in "Brazilian keratin type" hair-straightening products: a cross-sectional study. J Am Acad Dermatol. 2014 Abstract
  15. Couto AC, Ferreira JD, Rosa AC, Pombo-de-Oliveira MS, Koifman S; Brazilian Collaborative Study Group of Infant Acute Leukemia. Pregnancy, maternal exposure to hair dyes and hair straightening cosmetics, and early age leukemia. Chem Biol Interact. 2013 Abstract Full text (link to original source) Full text (in our servers)
  16. Weathersby C, McMichael A. Brazilian keratin hair treatment: a review. J Cosmet Dermatol. 2013 Abstract
  17. Monakhova YB, Kuballa T, Mildau G, Kratz E, Keck-Wilhelm A, Tschiersch C, Lachenmeier DW. Formaldehyde in hair straightening products: rapid ¹H NMR determination and risk assessment. Int J Cosmet Sci. 2013 Abstract
  18. Pierce JS, Abelmann A, Spicer LJ, Adams RE, Glynn ME, Neier K, Finley BL, Gaffney SH. Characterization of formaldehyde exposure resulting from the use of four professional hair straightening products. J Occup Environ Hyg. 2011 Abstract
  19. Mazzei JL, Figueiredo EV, da Veiga LJ, Aiub CA, Guimarães PI, Felzenszwalb I. Mutagenic risks induced by homemade hair straightening creams with high formaldehyde content. J Appl Toxicol. 2010 Abstract
  20. Galiotte MP, Kohler P, Mussi G, Gattás GJ. Assessment of occupational genotoxic risk among Brazilian hairdressers. Ann Occup Hyg. 2008 Abstract

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