What is permanent hair straightening?
Using chemicals to permanently cause hair to straighten.
It's also known as Relaxer or Keratin treatment.
What does permanent hair straightening do?
- Head hair
Straightens and slightly lengthens
How long does permanent hair straightening last?
Permanent hair straightening lasts for around three months before it needs to be reapplied.
What should I be aware of?
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 1.
Stylists may not realise which ingredients are contained in some permanent straightening treatments and underestimate the danger to themselves and their clients 2. Always ensure you discuss with your stylist what treatments are being applied and what ingredients they contain.
While called permanent hair straightening, treatment needs to be reapplied around every 12 weeks 3.
What kinds are there?
Permanent hair straighteners can use different types of chemicals to perform the straightening.
In curly hair, the proteins that the hair is made from are held in a curled shape by chemical bonds that can be broken by chemicals called “relaxers”. With these bonds broken, the hair become straight straight. The different kinds of relaxers are:
hydroxides, which are strong alkalis such as sodium hydroxide or guanidine hydroxide. This process of breaking chemical bonds is called lanthionization 4. 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 1. Stylists may not realise which ingredients are contained in keratin treatments and underestimate the danger to themselves and their clients 2.
Are there other options?
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.
- 1.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. Link
- 2.Weathersby, Courtney and McMichael, Amy (2013) “Brazilian keratin hair treatment: a review.” Journal of cosmetic dermatology, 12(2), pp. 144–148. Link
- 3.Dias, Maria Fernanda Reis Gavazzoni (2015) “Hair cosmetics: an overview.” International journal of trichology, 7(1), p. 2. Link
- 4.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. Link
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