High affinity inhibitor for cathepsin L, cathepsin L2 (cathepsin V), and legumain (PubMed:30425301). Involved in the regulation of epidermal cornification, and hair follicle morphogenesis and maintenance (PubMed:30425301). Restricted to the stratum granulosum of normal skin, the stratum granulosum/spinosum of psoriatic skin, and the secretory coils of eccrine sweat glands. Low expression levels are found in the nasal cavity. Substrate for transglutaminases. Acts as an acyl acceptor but not as an acyl donor. The disease may be caused by variants affecting the gene represented in this entry. Belongs to the cystatin family.