What effects does it have?
- Head hair
Straightens and slightly lengthens
What is it?
Using chemicals to permanently cause hair to straighten.
It's also known as Relaxer or Keratin treatment.
How long does it last?
Permanent hair straightening lasts for around three months before it needs to be reapplied.
Stylists may not realise which ingredients are contained in some permanent straightening treatments and underestimate the danger to themselves and their clients 1. Always ensure you discuss with your stylist what treatments are being applied and what ingredients they contain.
Hair is made from keratin proteins. In curly hair, these keratin proteins are held into a curled shape by chemical bonds.
These bonds can be broken, straightening the hair. This is done by different types of chemicals known as chemical relaxers:
hydroxides, which are strong alkalis such as sodium hydroxide or guanidine hydroxide. This process of breaking chemical bonds is called lanthionization 2. To prevent the strong alkali attacking the scalp, it is useful to apply Vaseline along the hair line and on the ears. You should also carefully rinse off the chemicals after use. These chemicals are not suitable for straightening bleached hair and dying hair after chemical straightening can be difficult without damaging the hair 3.
thioglycolates, such as ammonium thioglycolate. These chemicals must be followed by treatment with a hot straightening iron and hydrogen peroxide solution. These chemicals are not suitable for straightening bleached hair and dying hair after chemical straightening can be difficult without damaging the hair 3.
aldehydes, often called “keratin treatment” or “Brazilian treatment”. Keratin treatments have often contained dangerous cancer-causing chemicals such as formaldehyde or glutaraldehyde, even when labelled “formaldehyde free”. They may also contain methylene glycol, also known as methanediol, a chemical which releases formaldehyde when heated 4. Stylists may not realise which ingredients are contained in keratin treatments and underestimate the danger to themselves and their clients 1.
An alternative to chemical straightening is to break the chemical bonds by hair straightening using heat. This approach only lasts until the hair becomes wet, so is much more of a temporary solution.
Repeated chemical straightening of hair carries a number of risks, including itching, burns and scars on the scalp, thinning and weakening of the hair shaft, discolouration and hair loss, and allergic reactions 4.
While called permanent hair straightening, treatment needs to be reapplied around every 12 weeks 3.
- 1 Weathersby, Courtney and McMichael, Amy (2013) “Brazilian keratin hair treatment: a review.” Journal of cosmetic dermatology, 12(2), pp. 144–148.
- 2 Sá Dias, Tania Cristina de, Baby, André Rolim, Kaneko, Telma Mary and Robles Velasco, Maria Valéria (2007) “Relaxing/straightening of Afro-ethnic hair: historical overview.” Journal of cosmetic dermatology, 6(1), pp. 2–5.
- 3 Dias, Maria Fernanda Reis Gavazzoni (2015) “Hair cosmetics: an overview.” International journal of trichology, 7(1), p. 2.
- 4 Miranda-Vilela, AL, Botelho, AJ and Muehlmann, LA (2014) “An overview of chemical straightening of human hair: technical aspects, potential risks to hair fibre and health and legal issues.” International journal of cosmetic science, 36(1), pp. 2–11.
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Page last updated: September 2017