Steroid sulfatase (STS), or steryl-sulfatase, formerly known as arylsulfatase C, is a sulfatase enzyme involved in the metabolism of steroids. It is encoded by the STS gene. This gene encodes a multi-pass membrane protein that is localized to the endoplasmic reticulum. It belongs to the sulfatase family and hydrolyzes several 3-beta-hydroxysteroid sulfates, which serve as metabolic precursors for estrogens, androgens, and cholesterol. Mutations in this gene are associated with X-linked ichthyosis (XLI). Alternatively spliced transcript variants resulting from the use of different promoters have been described for this gene.