Sodium Lauryl Sulphate

What is SLS?

Sodium Lauryl Sulphate (SLS) is a synthetic detergent, cleaning agent and anionic surfactant (substance that makes bubbles), used in many cleaning and hygiene products. SLS is derived from cheap coconut and palm oils that in combination with its high detergent properties make substance the most popular and useful from a whole range of surfactants. SLS is available commercially in powder and pallet forms. In water the pallet form dissolves faster than the powder form.

Why is it used everywhere?

Because it is cheap, SLS is widely utilized as one of the ingredients of detergent for laundry. Due to its highly effective cleansing qualities it is used in any task requiring the removal of oil stains, hence high concentration of the substance is found in engine degreasers, floor cleaners and car washing soaps. For its thickening effects and its ability to create lather SLS is added to liquid soaps, bubble baths, body wash, shampoos and oral hygiene products. Also today SLS obtains popularity in products such as scrubs, shaving creams, hair sprays, make-up removals where it provides a foaming effect. However the foaming effects of soaps do not improve the ability to clean. It is added for visual reasons.

History

SLS was developed during World War II as a synthetic alternative to soap, because the natural ingredients such as animal fats, used to make soap, were in a short supply. Because of its high detergent and grease cleaning properties SLS found its high usage in washing and cleaning navy machines, such as tanks, armoured personnel carriers and aircrafts. Since 1947th in France and later since 1949th in Great Britain and USA, SLS became integral part of the laundry detergents.

After 1952, the manufactures started using it in shampoos. Since a second half of 80s SLS became highly popular among the manufactures of the makeup and the cosmetic industry as a whole. This included: acne treatment, hand and face cream, mascara, around-eye cream, lip balm and eye-liner. During the next decade even some eczema treatments, damaged skin treatments and rash creams contained SLS.

Laboratory Application

In science it is commonly used to prepare the proteins for electrophoresis in SLS-page technique. This compound disrupts non-covalent bonds in the proteins, in turn denatured molecules of proteins lose their usual shape, which increases negative charge of the proteins.  In medicine SLS has also found a usage in the analysis of haemoglobin. Sodium Lauryl Sulphate combines with the oxidized iron sub-unit in haemoglobin creating a stable product which then can be analysed.

Why is there a worry about SLS?

As all lathers and detergents, SLS extracts oils from the skin, in turn this process may cause irritation of skin, as a result causing inflammation (dermatitis). The main symptoms are: dryness, soreness and redness of the skin.

The extent and deepness of irritation caused by SLS depends on: a time during which it comes in a contact with the skin; its concentration in a product and frequency of usage. At the end of the 90s and at the beginning of 2000s some media sources actively speculated on a topic of the danger of SLS, especially its links to the skin cancer and blindness. However these rumours remained not proved. In 2002 in the US the Cosmetic Ingredient Review (CIR) assessed the ingredient for safety in several tests and reported that SLS appears to be safe in skin care products that are applied briefly to the skin and then rinsed off. 

Who should worry about SLS?

According to the several studies conducted by the International Eczema Society and European Paediatric Society for the last three years, there are two groups of people which are most subjected to the influence of SLS: children up to 10 years and people suffering  from aphthous ulcer. The epidermis (outer layer of the skin) is thinner in children than in adults. For this reasons the skin of children is more sensitive to SLS than of adults. There have been several studies that showed the patients had significant aphthous ulcers after using SLS-containing toothpaste, compared with the people using SLS-free toothpaste. Moreover, patients using the SLS-free toothpaste experienced faster healing of ulcers and less ulcer-related pain in average than patients using SLS-containing toothpaste.

What can we do?

When choosing bath or skin care products for a child, it is recommended to pick products that are specially formulated for babies or children. They contain substances that are milder and gentler than SLS, which are derived from sugar. I would also advise not to apply SLS-containing products to skin for a long time and rinse them off as soon as possible. Hence you can reduce the time of influence of SLS on skin as well as prevent any possible irritation.

Do not use products containing SLS if you or your children have eczema or sensitive skin. You can buy SLS-free soaps at most chemists. Although they do not foam, they are just as effective at cleaning the skin. However, SLS-free products cost more than "traditional" formulations.