Activates STAT3 and possibly STAT1 and STAT5 through the IL31 heterodimeric receptor composed of IL31RA and OSMR (PubMed:15184896). May function in skin immunity (PubMed:15184896). Enhances myeloid progenitor cell survival in vitro (PubMed:17379091). Induces RETNLA and serum amyloid A protein expression in macrophages (PubMed:25847241). Il31 transgenic mice develop dermatitis. A similar phenotype is caused by local delivery of Il31.