Sodium lauryl sulphate (SLS) is reported to be the most frequent of eye irritants in shampoos. It is a cleansing and foaming agent used in a range of personal care and household products. SLS can damage the protective outer layer of the skin and has been shown through research to penetrate the skin to depth of 5-6mm (1/4 inch) causing skin irritation with deeper transference occurring via the bodily systems. SLS is commonly used in laboratory testing on humans and animals to induce skin irritation so that the healing or modifying properties of other substances can be measured.

Skin is also sometimes irritated by SLS in tests to increase the penetration of other substances. Using SLS via cosmetics and personal hygiene products could potentially allow other toxicants to penetrate the skin more easily. Toothpastes often contain SLS in order to clean the teeth and mouth more efficiently, even though the substance has been reported to irritate mucous membranes in sensitive individuals. In the US, children’s foaming bath products carry a health warning alerting parents to this.

Formaldehyde is used as a preservative in nail polishes, soaps and other cosmetic products. It is also found in household products such as furniture polish. It is a suspected carcinogen and common skin and eye irritant. The international agency for research on cancer (IARC) says there is evidence that formaldehyde causes a form of throat cancer in humans. Although the US Food and Drug Administration (FDA) does not object to the use of formaldehyde in cosmetics, providing certain restrictions are adhered to, finished products containing it in the EU must be labelled with the warning, ‘Contains Formaldehyde’ if the concentration exceeds 0.05 per cent. It is one chemical you are well advised to avoid given its potential to cause allergies and irritation. Seek alternatives wherever possible.