Ammonium Lauryl Sulfate
In plain terms
A harsh foaming sulfate, the ammonium-salt sibling of SLS. It cleans and lathers well but is a concentration-dependent irritant that can dry and disrupt the skin barrier. Not a carcinogen and not an allergen, despite old internet claims, but easy to do better than.
What the evidence shows
Ammonium lauryl sulfate, or ALS, is an anionic sulfate surfactant closely related to sodium lauryl sulfate (SLS), used for its strong foam and cleansing in shampoos and washes. Unlike sodium laureth sulfate, it is not ethoxylated, so it does not carry the 1,4-dioxane concern that comes with the laureth versions. Its real drawback is irritation: like SLS, it is a primary irritant whose effect rises with concentration and contact time. Below about 1 percent it is essentially non-irritating, but at the higher levels used in many cleansers it can leave skin and eyes dry, tight, and stripped, especially with prolonged contact, which is why the safety panel cleared it mainly for brief, rinse-off use. Two myths are worth clearing: ALS is not a carcinogen, a claim that has circulated about sulfates for years without support, and it is not a skin sensitizer, so it causes irritation rather than true allergy. None of that makes it a good pick for sensitive or dry skin, and since much gentler surfactants exist, like the isethionates and the glucosides, this lands as one to avoid when you can.
On the label
Listed as ammonium lauryl sulfate or ALS. If your skin or scalp runs dry, sensitive, or easily irritated, look for a gentler cleanser built on sodium cocoyl isethionate or an alkyl glucoside instead. In a quick-rinse shampoo it is less of an issue than in anything left on the skin.