Kit ligand, also known as Hematopoietic growth factor KL, Mast cell growth factor, Steel factor, Stem cell factor, c-Kit ligand, Kitlg and KITL, is a single-pass type I membrane protein that belongs to the SCF family. KITL / kit ligand also belongs to the family of dimeric transmembrane growth factors. The soluble form of KIT ligand is a secreted protein. Mast cells are thought to participate in a variety of immune responses, such as parasite resistance and the allergic reaction. Mast cell development depends on stem cell factor (Kit ligand) and its receptor, c-Kit. KITL / kit ligand stimulates the proliferation of mast cells. KITL / kit ligand is able to augment the proliferation of both myeloid and lymphoid hematopoietic progenitors in bone marrow culture. Efficient cell surface presentation of KITL / kit ligand is essential for the migration, proliferation, and survival of melanocytes, germ cells, hemopoietic stem cells, and mastocytes. KITL / kit ligand acts synergistically with other cytokines, probably interleukins. KITL / kit ligand plays a crucial role in the development and maintenance of the melanocyte lineage in adult skin. It exerts permanent survival, proliferation and migration functions in Kit receptor-expressing melanocytes. KITL / kit ligand misexpression in some hyperpigmented lesions may open the avenue for Kitl-dependent treatment of pathological skin conditions.