Why Reading Hair Dye Labels Is Important To Your Hair

There are many different types of hair coloring products on the market today with demi-permanent, semi-permanent and permanent options to choose from. Drugstores and beauty supply store walls are lined with a variety of hair dyes. But how does hair dye work? Are there any harmful ingredients to avoid?

High molecular weight is the key to demi-permanent hair dye. High molecular weight prevents dye from penetrating into the cuticle, the outer layer of a hair shaft1. This allows for dye to easily wash out. Dyes with low molecular weights, like semi-permanent and permanent hair dyes, can readily pass through the cuticle and into the hair cortex1. This allows the dye to stay longer. Permanent hair coloring is the most effective with gray hair with semi-permanent coloring lasting up to 12 washes. Demi-permanent dye can be great for previously colored hair and lasts up to 2 months. Damage to the cuticle, cortex (thickest hair layer) and/or medulla (innermost layer of the hair shaft) can occur when using certain dye ingredients2.

An ingredient to be weary of is p-phenylenediamine or PPD for short. This hair dye ingredient can be associated with allergic reactions and hair damage3. In order to determine if you might react to this hair dye ingredient, patch testing can be performed4. A patch test involves testing the skin with a small amount of the dye to see if a skin reaction takes place. Positive patch tests for PPD are rare but have been found across Asia, Europe and North America, making up 4 to 6% of patch test results5.

As hair coloring products are chemically treating your hair, there are some steps that can be taken to protect against possible skin reactions. Nitrile gloves can provide protection, including against PPD skin reactions6. Additionally, Health Canada has made it mandatory that all hair dyes that have PPD as an ingredient include skin sensitivity warnings and specific instructions on packaging to help avoid a reaction7.

If you would like to color your hair but aren’t exactly sure what hair dyes you should use, speak to your hair consultant for more information.

Article by: Sarah Versteeg MSc, Mediprobe Research Inc. 

  1. Larsen WG, Jackson EM, Barker MO, Bednarz RM, Engasser PG, O’Donoghue MN, et al. A primer on cosmetics. AAD Advisory Board, CTFA Task Force on Cosmetics. J Am Acad Dermatol. 1992 Sep;27(3):469–84.
  2. Ahn HJ, Lee W-S. An ultrastuctural study of hair fiber damage and restoration following treatment with permanent hair dye. Int J Dermatol. 2002 Feb;41(2):88–92.
  3. Zanoni TB, Hudari F, Munnia A, Peluso M, Godschalk RW, Zanoni MVB, et al. The oxidation of p-phenylenediamine, an ingredient used for permanent hair dyeing purposes, leads to the formation of hydroxyl radicals: Oxidative stress and DNA damage in human immortalized keratinocytes. Toxicol Lett. 2015 Dec 15;239(3):194–204.
  4. Choi Y, Lee JH, Kwon HB, An S, Lee A-Y. Skin testing of gallic acid-based hair dye in paraphenylenediamine/paratoluenediamine-reactive patients. J Dermatol. 2016 Jul;43(7):795–8.
  5. Thyssen JP, White JML, European Society of Contact Dermatitis. Epidemiological data on consumer allergy to p-phenylenediamine. Contact Dermatitis. 2008 Dec;59(6):327–43.
  6. Antelmi A, Young E, Svedman C, Zimerson E, Engfeldt M, Foti C, et al. Are gloves sufficiently protective when hairdressers are exposed to permanent hair dyes? An in vivo study. Contact Dermatitis. 2015 Apr;72(4):229–36.
  7. Consumer Product Safety – Safety of Cosmetic Ingredients [Internet]. Health Canada. 2016 [cited 2016 Jul 12]. Available from: http://www.hc-sc.gc.ca/cps-spc/cosmet-person/labelling-etiquetage/ingredients-eng.php#a4.11