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The Toxic Chemicals in Shampoo

Boy with shampoo in hair

Cosmetic and personal care products are still among the least regulated products in most countries with many untested ingredients being assumed to be safe. The regulatory authorities occasionally express concern about this state of affairs, but little action to date has been taken. As you will see there is a good reason why bottles of shampoo are required to carry a warning label suggesting that you avoid contact with the eyes and rinse thoroughly with water if you are unfortunate enough to actually get some of the product in your eyes!


What is shampoo?

Fundamentally, shampoo is a mixture of a detergent (surfactant) and water designed to remove the greasy sebum that forms at the shaft along with the dirt it attracts, but without stripping the hair of all its natural oils. Shampoos contain the following ingredients:

  • Foaming agents
  • Foam boosting agents
  • Preservatives
  • Modifiers
  • Colourants
  • Fragrance


Intentional ingredients in shampoo

Foaming agents in shampoos

Whilst shampoos don’t need to foam to work, consumers over the years have come to associate foaming power with cleansing. Sodium Lauryl Sulphate (SLS) is the foaming agent that is used in about 90% of shampoos with Sodium Laureth Sulphate (SLES) found in about 20% of products and added to improve lather. Sodium Lauryl Sulphate is such a strong detergent that it is used to degrease engines and clean airport runways! This toxic chemical penetrates the skin and remains detectable in the body for up to 5 days after use. Sodium Lauryl Sulphate also poses a direct danger to the eyes and can accumulate within the eye possibly causing cataracts. It is a known carcinogen in humans, enhances allergic reactions to other agents and accumulates particularly in the heart, liver, lungs and brain.

Less commonly either Ammonium Lauryl Sulphate or Sodium Myreth Sulphate are used as foaming agents in shampoos for dry or damaged hair or in clear shampoos.


Foam boosting agents in shampoos

Sometimes, foam boosters such as cocamide monethanolamine (MEA), diethanolamine (DEA) or triethanolamine (TEA) are added to shampoos. Cocamide DEA is a toxic chemical which is known to cause kidney and liver damage and cancer in animals and is considered to pose a serious health risk and be a possible carcinogen in humans. This is a concern because of the widespread nature of the use of these chemicals in shampoo leading to widespread exposure.


Preservatives in shampoos

One or two preservatives are required for the water soluble component of the shampoo and others for the oil soluble component. These agents are toxic - biocidic (literally: anti-nature) - which is why they are useful as preservatives. The toxic paraben family of chemicals are often used along with methylchloroisothiazolinone and methylisothiazoline (MIT) which has been shown to cause neurological damage in rats and is a potent irritant and allergen. There is particular concern that the use of these toxic chemicals by pregnant women may adversely affect foetal brain development and may also be a factor in the the development of Alzheimer's disease.

Formaldehyde DMDM hydantoin, diazolidinyl urea and imidazolidinyl urea are all preservatives that are used for the water soluble component of shampoos that release formaldehyde. This is known to be a potent skin, eye and lung irritant with one in five people exposed to formaldehyde-containing products experiencing an allergic reaction for which reason its use as an ingredient has been banned in Sweden and Japan (Environmental Health Perspectives, December 2002). Exposure to toxic formaldehyde is also known to cause joint pain, depression, headaches, chest pain, ear infections, chronic fatigue, dizziness, insomnia and to cause cancer in both animals and humans. There is also concern that, at current levels of toxin exposure, it can cause DNA damage to sperm.


Modifiers in shampoo

Smoothing agents related to glycerol propylene glycol are also often used in shampoo and are closely chemically related to car radiator antifreeze and are, unsurprisingly, highly irritant and toxic. Some of the adverse effects attributed to propylene glycol include various skin disorders including dermatites, dry skin and rashes, kidney and liver abnormalities and cell membrane damage.

Various oils and synthetic silicone polymers can also be added to shampoo to aid smoothing of the cuticle of the hair shaft along with thickeners such as xanthan gum and emulsifiers such as glycol stearate.


Colourants in shampoo

Toxic colourings derived from coal tar are often added to shampoos and these are known to cause allergic reactions and to cause cancer in animals. A variety of thickeners and opacifiers can also be added to change the consistency, appearance and qualities of the shampoo. For instance, the pearlescent effect of some shampoos is achieved by adding flakes of wax.


Fragrance in shampoo

A selection of 4,000 separate artificial and natural ingredients can be added to fragrance shampoos. In a 1989 study conducted by the US Institute of Occupational Safety and Health, one third of these fragrances were found to be toxic. These fragrances are known to cause rashes and skin discolouration, headaches and dizziness, coughing or vomiting and to affect the central nervous system causing hyperactivity, depression, irritability and an inability to cope. In a study in 1989 by the US Environmental Protection Agency, all perfumes were found to contain toluene which is known to be toxic to the developing foetus, and to cause liver, kidney and brain damage. Phthalates are also often added to shampoos for their ability to enhance fragrance or as a solvent and these are potent toxic endocrine and metabolic disruptors that are found almost universally in blood, urine and especially breast milk.


Unintentional ingredients in shampoo

The following chemicals are considered to be contaminants of shampoo and so are not required to be listed on the label.

1, 4 dioxane Harsh detergents can be cheaply treated with ethylene oxide to produce a milder detergent action and this process generates 1, 4 dioxane as a by-product. One study found 1, 4 dioxane in over half of all body care products and this is a concern because it is closely related to dioxin which is the most toxic chemical known. 1, 4 dioxane is recognised to penetrate the skin; irritate both the eyes and respiratory tract; is suspected of being toxic to the central nervous system, liver, kidneys, breast and reproductive organs; is recognised to cause cancer in animals and is a suspected carcinogen in humans.

Nitrosamines The foam boosting agent, cocamide DEA (see above) which is often added to shampoo is known to react with nitrosating agents (formed either by the addition of nitrite preservatives, degradation of other ingredients or exposure to air) to form nitrosodiethanolamine (NDEA). Studies have identified toxic nitrosamines in over half of all body care products tested. They are potent carcinogens which can penetrate the skin and for this reason some manufacturers test their finished products for nitrosamines.

Finally, as if that cocktail of toxic chemicals weren’t enough food for thought: dioxin may leach from the plastic bottle into the shampoo!

The take-home message? Look at labels and make sure the the products you are buying are truly natural!


Further resources

Books on this topic include Cosmetics Unmasked and Home Safe Home listed under Natural Recovery in the Recommended Reading section. For an explanation of the importance of toxicity and detoxification, please refer to The Natural Recovery Plan book.

You might also be interested in the following: 

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What's in Hair Dye?

Lead in Lipstick?

The Health Risks of Fluoride

Understanding Skin Care

Botox and Fillers: The Case Against

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The Ugly Surprise Inside Many Skin Care Products listed under Natural Recovery in the Audio Hub

Or for all media use the Search facility at the top of the page


The toxic chemicals in shampoo: Article summary

This article addresses the many synthetic foaming agents, foam-boosting agents, preservatives, modifiers and fragrances used in shampoo and their impact upon health.


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The Natural Recovery Plan Newsletter February 2010 Issue 2. Copyright Alison Adams 2010. All rights reserved
Dr Alison Adams Dentist, Naturopath, Author and Online Health Coach

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