depilatory (dĭpĭlˈətôrˌē) [key], substance used to remove hair. In preparing hides for tanning, lime is the chief depilatory. For the removal of superfluous hair from the human body, metal sulfides such as barium sulfide, sodium sulfide, calcium hydrosulfide, and strontium hydrosulfide are used. The powdered material is usually combined with other substances (lime, sugar, chalk, perfume) and made into a paste which is spread on the skin. The hair is dissolved into a gelatinous mass and is removed along with the paste. However, these reagents do not prevent regrowth of hair and are potentially dangerous. Wax depilatories that harden on the skin and pull up the hair by the roots when peeled off delay but do not prevent regrowth of hair. The only permanent method of removing hair is by cosmetic electrolysis, in which a weak electric current, passing through a needle, destroys the hair follicle.