Sodium lauryl sulphate (SLS) is an anionic surfactant (detergent) which is included as a foaming agent (to clean and make bubbles) in a huge variety of commonly used products. These include shampoos, soaps, face and body washes, toothpaste, washing up & laundry detergents and also industrial cleansing chemicals such as engine degreasers. There are many derivatives of SLS that can be found in commercial preparations, including sodium laureth sulphate, sodium laureth-3 sulphate, and DEA or tea sodium lauryl sulphate. Although these derivatives may vary slightly in mildness, the general action and effects are essentially similar.

Growing Concern

Recently, there has been growing concern about the widespread use of these detergents and their safety has been called into question. In this report, we will review the scientific literature available and show why it may be wise to attempt to minimise your exposure to this family of foaming agents.

A major concern about SLS is the effect that it has when used in combination with other ingredients commonly found in personal care products. SLS has the potential to react with other ingredients (e.g. 2-bromo-2-nitropropane-1,3-diol, DEA, MEA, TEA) to form nitrosating agents, which in turn can form nitrosamines, which are known to be carcinogenic.

Similar names, different effects

There are several other surfactants with similar names to SLS - in particular ammonium lauryl sulphate and ammonium laureth sulphate. Although these sound very similar their molecular structure is significantly different and they do not have the same potential to irritate the skin. Also, because their molecules are larger than those of SLS, they are not able to pass through the skin and therefore cannot be absorbed into the body in the same way. Because of these differences, ammonium lauryl and laureth sulphates are considered to be milder and safer alternatives to SLS.

Effects of SLS on the Skin

• SLS is commonly used in research laboratories as the standard ingredient (upon which all other substances are compared to) for irritating the skin.
• A solution of just 2% SLS can increase skin thickness, cause irritation, inflammation (1) and increase other forms of immune activity in the skin (2). Some shampoos can contain more than 50% SLS.
• SLS can cause an increase in enzyme levels in the skin, leading to redness and swelling (3). It can also lead to dryness, roughness and even flaking of the skin.

Effects of SLS in the Mouth

• SLS can damage the delicate mucosal membranes in the mouth, causing the separation of epithelial layers from the mucosa (4).
• Burning and severe itching of the oral mucosa following the application of SLS containing toothpaste has been reported (4).
• The tissue damage caused by SLS increases with increasing concentration of SLS (4).
• Switching from a toothpaste containing SLS to one without, can lead to a statistically significant decrease in the occurrence of mouth ulcers in those with recurrent aphthous ulcers (5, 6).

Effects of SLS on the Eyes

• SLS can penetrate the cornea of the eye (even if absorbed through the skin), accumulate readily and is released slowly. These effects are greater in younger individuals (7). A single drop of SLS can remain in the body for 5 days, so if you wash a childs hair more than once a week with a SLS containing shampoo, there will be constant levels of SLS present.
• A solution of 1.3% SLS can reduce the rate of healing in the eye (8).

Variations in response to SLS

• There is substantial inter-individual variability in the response to SLS  not everybody will be affected to the same extent (9).
• Younger individuals are more susceptible to the effects of SLS (10, 11).
• The effects of SLS become more harsh with increasing temperature (12). This is important to note, as most people prefer to wash in warm water.

References

1. ANDERSON C, SUNDBERG K, GROTH O. Animal model for assessment of skin irritancy. Contact Dermatitis 1986 Sept: 15 (3): 143-51.
2. LINDBERG M, FARM G, SCHEYNIUS A. Differential effects of sodium lauryl sulphate and non-ionic acid on the expression of CD1a and ICAM-1 in human epidermis. Acta Derm Venereol 1991: 71 (5): 384-8.
3. GIBSON WT, TEALL MR. Interactions of C12 surfactants with the skin: Changes in enzymes and visible and histological features of rat skin treated with sodium lauryl sulphate. Food Chem Toxicol 1983 Oct: 21 (5): 587-94.
4. HERLOFSON BB, BARKVOLL P. Oral desquamation caused by two toothpaste detergents in an experimental model. Eur J Oral Sci 1996: 104:21-26.
5. HERLOFSON BB, BARKVOLL P. Sodium lauryl sulphate and recurrent aphthous ulcers. preliminary study. Acta Odontol Scand 1994 Oct: 52(5):257-9.
6. CHAHINE L, SEMPSON N, WAGONER C. The effect of sodium lauryl sulphate on recurrent aphthous ulcers: A clinical study. Compend Contin Educ Dent 1997: 18 (12): 1238-40.
7. CLAYTON RM, GREEN K, WILSON M, ZEHIR A, JACK J, SEARLE L. The penetration of detergents into adult and infant eyes: Possible hazards of additives to ophthalmic preparations. Food Chem Toxicol 1985 Feb: 23 (2): 239-46.
8. GREEN K, JOHNSON RE, CHAPMAN JM, NELSON E, CHEEKS L. Preservative effects on the healing rate of rabbit corneal epithelium. Lens Eye toxic Res 1989: 6 (1-2): 7-41.
9. BASKETTER DA, GRIFFITHS HA, WANG XM, WILHELM KP, MCFADDEN J. Individual, ethnic and seasonal variability in irritant susceptibility of skin: The implication for a predictive human patch test. Contact Dermatitis 1996: 35 (4): 208-13.
10. HERLOFSON BB, BARKVOLL P. Oral mucosal desquamation of pre- and post-menopausal women. A comparison of response to sodium lauryl sulphate in toothpastes. J Clin Periodontol 1996 Jun: 23 (6): 567-71.
11. SCHWINDT DA, WILHELM KP, MILLER DL, MAILBACH HI. Cumulative irritation in older and younger skin: A comparison. Acta Derm Venereol 1998: 78 (4): 279-83.
12. GOFFIN V, LETAWE C, PIERARD GE. Temperature-dependant effect of skin-cleaning products on human stratum corneum. J Toxicol 1996: 15 (2): 125-30.