Skip to main content

Do you really know how many toxic ingredients you spread over your hair on a daily basis? Maybe it’s time to take a closer look at what’s inside your shampoo or conditioner, the one you use everyday. In fact, there are dozens of different chemicals in hair products. As citizens, we think that it can’t be an issue. We assume regulations around the cosmetic industry protect us from harmful molecules. While this is not false, this is not true either. Let’s discover the worst chemicals that live in your favorite hair products.

Worst Chemicals in Hair Products

Hair products are not only applied directly on the scalp, but onto the whole body (think when you’re under the shower). It’s inevitable that particles eventually get absorbed by our skin. The small quantity of these chemicals found in each product may not be a concern in the short run. On the long run however, dozens of chemicals in hair products accumulate in your system, leading to potential side effects.

According to a 2004 study, “one of every 13 women and one of every 23 men – are exposed to ingredients that are known or probable human carcinogens every day through their use of personal care products” – Source: EWG

Each of the chemicals listed below has a growing list of evidence that show long-term health issues like cancer, hormonal dysfunctions and other different possible diseases. Although we focus on hair products only in this article, it’s worth mentioning all the chemicals listed can be found in other personal care and household products.


1,4-dioxane chemical structure
1,4-dioxane is an industrial chemical that can be found in 22% of cosmetics products. But it may be absent from ingredient lists! That’s because 1,4-dioxane is a contaminant produced when ingredients mixed together react to form a compound. But when applied with certain preparations such as lotions, 1,4-dioxane penetrates the skin easily. Exposed in high quantities, 1,4-dioxane is a potential human carcinogen and is listed as an animal carcinogen by the National Toxicology Program. It is also linked to severe kidney and liver diseases.

  • Hair Products: shampoos, hair relaxers, any liquid soap
  • On the Ingredient List: “PEG compounds”, “PEG”, “polyethylene”, “polyethylene glycol,” “polyoxyethylene”, “diethylene dioxide”, “diethylene ether”, “dioxane”, “1,4-dioxane,” and “p-dioxane”, “sodium laureth sulfate”
  • Potential Health Problems: from eye and nose irritation to potential organ toxicity and cancer
  • At-Risk Populations: infants, teenagers, pregnant women and animals

Butylated Compounds

Butylated hydroxytoluene (BHT) chemical structure
Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are derivative of phenol (phenolic compounds), prized for their antioxidant properties and used as preservatives in different hair care products. They are also largely used in the food industry. But there are concerns about their safety. BHA and BHT are connected to cases of endocrine disruption, organ-system toxicity, and other health problems. Note that BHA has been categorized as  a “high human health priority” by Health Canada.

  • Products: various hair products
  • On the Ingredient List: “BHA” and “BHT”
  • Potential Health Problems: endocrine disruption, developmental and reproductive toxicity, organ-system toxicity, cancer
  • At-Risk Populations: infants and pregnant women


Formaldehyde chemical structure
Formaldehyde and formaldehyde-releasing preservatives (FRPs) are particularly used  in shampoos. Used to help preventing microbes from developing in water-based products. formaldehyde can be easily absorbed through the skin and is linked to allergic skin reactions and even cancer.

  • Products: shampoos, baby shampoos and hair-smoothing products
  • On the Ingredient List: “formaldehyde”,  “polyoxymethylene urea”, “DMDM hydantoin”, “imidazolidinyl urea”, “diazolidinyl urea”, “glyoxal”, “sodium hydroxymethylglycinate” or “2-bromo-2-nitropropane-1,3-diol”.
  • Potential Health Problems: cancer and skin irritation
  • At-Risk Populations: infants and hair salon workers

Coal Tar

Coal chemical structure
Coal tar is produced during the incomplete combustion of coal and is a well-known carcinogen. Made of hundreds of compounds (e.g. polycyclic aromatic hydrocarbons or PAHs), coal tar can cause tumors and neurological damage. According to the American Academy of Dermatology Association (AAD), further scientific research is needed to know whether using coal tar on the skin can cause skin cancer. According to a federal regulation (FDA), any products must display a warning label if they contain coal tar at levels of 0.5% to 5%, and must indicate specific precautions for that product.

  • Products: Hair dyes, shampoos and scalp treatments
  • On the Ingredient List: “tar”, “coal tar solution”, “coal”, “crude coal tar”, “estar”, “lavatar”, “carbo-cort”, “impervotar”, “KC 261”, “picis carbonis”, “high solvent naphtha”, “naphtha distillate”, “naphtha”, “benzin B70”, or “petroleum benzin”
  • Potential Health Problems: cancer and organ system toxicity
  • At-Risk Populations: all

Ethanolamine Compounds (MEA, DEA, TEA)

Diethanolamine chemical structure
Ethanolamines are present in many hair products such as shampoos, hair conditioners and dyes. It is thought to cause eye and nose irritation, sore throat, headache, allergies, asthma and even liver tumors. According to the International Labor Organization (ILO), short-term exposure to ethanolamine is suspected to cause problems in the central nervous system. In Europe, diethanolamine (DEA) is prohibited in cosmetics by the European Commission.

  • Products: Shampoos, hair conditioners and hair dyes
  • On the Ingredient List: “diethanolamine”, “DEA”, “triethanolamine” “TEA”, “DEA-cetyl phosphate”, “DEA oleth-3 phosphate”, “oleamide DEA”, “lauramide DEA”, “linoleamide MEA”, “myristamide DEA”, “TEA-lauryl sulfate”, “stearamide MEA, “cocamide DEA” or “cocamide MEA”
  • Potential Health Problems: cancer and organ system toxicity
  • At-Risk Populations: all

Methylisothiazolinone and Methylchloroisothiazolinone

Methylisothiazolinone chemical structure
Methylisothiazolinone (MIT) and Methylchloroisothiazolinone (CMIT) are preservatives that can be found in many hair products, and are linked to possible neurotoxicity, allergic reactions and lung toxicity.

  • Products: shampoo, baby shampoo, hair conditioner, hair spray and hair color
  • On the Ingredient List: “OriStar MIT”, “Microcare MT”, “MI”,  “MCI”, “2-methyl-4-isothiazoline-3-one”, “5-Chloro-2-methyl-4-isothiazolin-3-one” or “Neolone 950 preservative”
  • Potential Health Problems: neuro-toxicity, allergies and inhalation toxicity
  • At-Risk Populations: individuals who are allergic to Methylisothiazolinone (MIT) or Methylchloroisothiazolinone (CMIT)


Octyl-methoxycinnamate chemical structure
Octinoxate (or Octyl methoxycinnamate – OMC), is used as a UV filter to protect the products from degrading when exposed to the sun. Knowing that octinoxate is an endocrine disruptor that mimics estrogen and can disrupt thyroid function, and is absorbed rapidly through the skin, you understand that . Unfortunately, octinoxate is approved for use in cosmetics throughout the world, the maximum authorized concentration depending on local legislation.

  • Products: shampoos and hair color
  • On the Ingredient List: “octinoxate”, “o methoxycinnamate (OMC)”, “escalol”, “2-ethylhexyl p-methoxycinnamate”, “parsol”, “parsol MCX”, or “parsol MOX”
  • Potential Health Problems: organ system toxicity, endocrine disruption, reproductive and developmental toxicity
  • At-Risk Populations: all


Paraben chemical structure
Parabens are preservatives used in a wide variety of personal care products and foods to prevent microbes from growing. These endocrine-disrupting chemicals may be absorbed not only through blood, but also by the digestive system and even through skin. Parabens have been found in breast cancer tissue and may play a role in breast cancer development.

  • Products: shampoos and hair conditioners
  • On the Ingredient List: “butylparaben”, “ethylparaben”, “isobutylparaben”, “isopropylparaben”, “methylparaben”, or “propylparaben”
  • Potential Health Problems: reproductive toxicity, cancer and endocrine disruption
  • At-Risk Populations: young children and pregnant women


Phenoxyethanol chemical structure
Phenoxyethanol is used as a preservative in hair products to limit bacterial growth. Reactions ranging from eczema to life-threatening allergic reactions are linked to phenoxyethanol. Also, infant oral exposure to phenoxyethanol can severely impact on certain nervous system functions.

  • Products: shampoos, hair conditioners, hair spray and hair color
  • On the Ingredient List: “phenoxyethanol”, “2-Phenoxyethanol”, “PhE” or “Euxyl K® 400”
  • Potential Health Problems: allergies and nervous system effects (infants)
  • At-Risk Populations: individuals allergic to phenoxyethanol and breast-feeding infants.


Quaternium-15 chemical structure
Quaternium-15, a known skin toxicant and allergen, may be especially dangerous when in contact for long periods of time. In the US, there are still no regulations for quaternium-15 use in hair products.

  • Products: Hair conditioners and hair styling products
  • On the Ingredient List: “Quaternium-15”, “benzalkonium chloride”, “benzethonium chloride”, “centrimonium bromide”, or “polyquaternium–n” (“n” being a number – i.e. “polyquaternium–3”).
  • Potential Health Problems: Irritation and sensitization
  • At-Risk Populations: all, but especially dangerous for hairdressers and janitors

Check Your Cosmetics’ Ingredients

If you are wondering about an ingredient’s toxicity in your everyday hair care product, make sure to use this Ingredient Checker tool 😉 Just type an ingredient, a product or a brand name in the search box and you’ll know everything about it!

Even if well-documented and carefully written, this content should not be used as a substitute for professional diagnosis and treatment. Consult a qualified health care provider before making any health care decisions about any specific medical condition.

Be Responsible. Share this Article.

Vincent P.

Humanist and animal's rights defender