sodium laureth sulfate

It is inexpensive detergent. Commonly used in cosmetic cleansers, hair shampoos, bath and shower gels, bubble baths, etc. - It is probably the most dangerous ingredient used in skin and hair-care products. In the cleaning industry SLS is used in garage floor cleaners, engine degreasers, car-wash soaps, etc. It is very corrosive and readily attacks greasy surfaces.

Sodium lauryl sulfate is used throughout the world for clinical testing as a primary skin irritant. Laboratories use it to irritate skin on test animals and humans so that they may then test healing agents to see how effective they are on the irritated skin.

Material safety data sheet for SLS:
http://www.healthy-communications.com/msdssodiumlaurylsulfate.html