IL-31 is a 24kD and 164 AA α-helical protein with a four-helix bundle structure, preferentially produced by CD 4+ type 2 helper T cells (Th2). IL-31 is closely related to the IL-6 type cytokines such as oncostatin M (OSM), Leukemia inhibitory factor (LIF) and cardiotrophin 1(CT-1). IL-31 signals via binding to a heterodimeric complex that is composed of IL-31 receptor A (IL-31RA) that is highly homologous with the gp 30-like receptor and oncostatin M receptor subunits. These receptor subunits are expressed in activated monocytes, in epithelial cells, and keratinocytes respectively. On target cells IL-31 binding can induce activation of the JAK/STAT, AKT and MAPK signaling pathways. Due to the ubiquitous expression of its receptor complex, IL-31 has numerous physiological roles including regulation of hematopoiesis and immune response. When overexpressed in transgenic mice, IL-31 induces severe pruritus resembling eczema in humans. Serum IL-31 was previously found overexpressed in adults with atopic dermatitis (AD).Serum measurement of IL-31 in paediatric atopic dermatitis revealed that elevated levels correlate with severity scoring. Activated effector T cells are recruited to the skin by chemokines and cell adhesion molecules. These components in the local microenvironment prolong T cell survival and contribute to the chronicity of these diseases. IL-31 is associated with the promotion of allergic and chronic inflammatory conditions such as dermatitis, pruritus, airway hypersensititvity and inflammatory bowel disease.