Hair dye and smoothers: what to check first

Do this

1. 1

   Patch test every colour before each use, following the timing on the box.

2. 2
   Skip black henna tattoos.Why

   Black henna is red henna plus the dye PPD.

3. 3

   Pick colour by lift and past damage, not by the word 'ammonia-free'.

4. 4

   Ask for a smoother's full ingredient list; avoid glyoxylic acid, linked to kidney injury.

5. 5

   What the science points to: ventilating during smoothing likely lowers fume exposure.

6. 6

   Itching, swelling or blisters after colour or smoother? Stop and talk to a doctor.

The numbers behind it

• 85%

  More damage in the most extreme case, monoethanolamine colour against ammonia colour, in a hair-colour maker's lab.

  Bailey 2014 ↗

• 9.3x

  Higher odds of PPD allergy after a black henna tattoo, among 10,425 Europeans (3.2% against 0.6%).

  Diepgen 2016 ↗

• 4 of 4

  Smoothers tested gave off formaldehyde or formaldehyde-forming compounds, including ones labelled formaldehyde-free.

  Pierce 2011 ↗

• 1.64x

  Higher uterine cancer risk after menopause with heavy relaxer use, in 44,798 Black women followed 1997 to 2019.

  Bertrand 2023 ↗

For your hair

• Box dye at home

  Patch test every time. In the European study, black henna was the main risk factor, not hair dye use itself.

• Teens and parents

  A holiday black henna tattoo is an easy route to dye allergy. Sensitised children may react to hair dyes later.

• Bleached or already coloured hair

  Each round adds damage. Stretch the gaps between colours and between chemical treatments.

• Relaxers and keratin smoothers

  Formaldehyde peaked during blow-drying in the salon test, so choose a ventilated room. Space out relaxers; long use went with uterine cancer after menopause.

Myths to ignore

• Myth Ammonia-free colour is gentler on hair.

  Truth In a lab comparison, monoethanolamine colour damaged hair more than ammonia colour on every measure, up to 85% more. Ammonia-free mostly means less smell.

  Bailey 2014 ↗
• Myth Black henna is just darker natural henna.

  Truth Black henna is red henna plus PPD, a strong sensitiser. About 1 in 40 people tattooed with it become allergic and can then react to hair dyes.

  de 2013 ↗
• Myth 'Formaldehyde-free' smoothers contain no formaldehyde.

  Truth Smoothers labelled formaldehyde-free still gave off formaldehyde or compounds that turn into it when heated, at levels that could reach workplace limits.

  Pierce 2011 ↗
• Myth Hair dye causes bladder cancer.

  Truth Pooling 17 studies gave a relative risk of 0.93 for personal hair dye use, and no extra risk even with the longest use.

  Turati 2014 ↗

Go deeper

• Bleach and colour damageBleaching and permanent dyeing chemically damage the hair fibre in every hair type, and most of that damage cannot be undone.
• Hair colour for looksGray hair lowered attractiveness ratings in image swaps and blonde versus brunette results conflict; dyeing damages hair, PPD allergy is the real dye risk, and personal dye use has not been shown to cause cancer.
• Relaxers, perms and smoothing treatmentsChemical straighteners and perms all damage hair, and some carry scalp, respiratory, kidney or cancer-association concerns worth knowing before you book.