Chemical Nasty : Sodium lauryl sulphate - Toxic Beauty

Sodium lauryl sulphate (SLS) is reported to be the most frequent cause of irritation by commercial shampoos. It is used in a range of personal care and household products as a cleaning agent and is also used as an industrial degreasant and floor cleaner. Sodium lauryl sulphate can damage the protective outer layer of the skin (stratum corneum) and is 'known to penetrate the skin and cause cutaneous irritation'.

Researchers at the Department of Dermatology, School of Medicine, University of California, found that sodium lauryl sulphate penetrated the skin directly to a depth of (5-6 mm a quarter of an inch) and deeper transference occurred via systemic redistribution (redistribution throughout the bodily systems).

It was suggested that underlying tissue, including the dermis, subcutaneous layers and muscle 'may be exposed to high levels of SLS'. Seven days after a single application of SLS to a hairless rat ,traces of the agent were identified in tissues.

Sodium lauryl sulphate and other surfactants (short for surface active agent) are commonly used in laboratory testing on humans and animals to induce skin irritation as a point of reference to measure the healing or modifying properties of other substances. As the Handbook of Detergents notes, 'surfactants may allow other toxicants to penetrate the skin'.

One study showed that 4 per cent SLS applied to the skin increased its permeability, with exposure to SLS at a concentration as low as 0.25 per cent for two hours enabling nickel to penetrate the skin. Repeated exposure to SLS can cause contact dermatitis in some individuals.

Toothpastes often contain SLS, even though it has been reported to irritate the mucous membranes in the mouth,' especially in individuals predisposed to recurrent mouth ulcers'.
When SLS undergoes ethoxylation to form the less abrasive detergent sodium laureth sulphate, the probable carcinogen 1,4-dioxane can be formed.

Sodium laureth sulphate is milder than sodium lauryl sulphate but can still cause skin irritation, especially in those who have pre-existing skin conditions.

Reference: Toxic Beauty: Dawn Mellowship