Steroid sulfates are endogenous sulfate esters of steroids. They are formed by steroid sulfotransferases via sulfation of endogenous steroids like cholesterol and steroid hormones. Although steroid sulfates do not bind to steroid hormone receptors and hence are hormonally inert, they can be desulfated by steroid sulfatase and in this way serve as precursors and circulating reservoirs for their active unsulfated counterparts. In addition, some steroid sulfates have biological activity in their own right, for instance acting as neurosteroids and modulating ligand-gated ion channels such as the GABA and NMDA receptors among other biological targets.