Epidermal growth factor (EGF) is the prototype of the large family of EGF-like proteins with a common structural motif comprising three intramolecular disulfide bonds. EGF is produced by various cell types like mammary gland cells, gut epithelial cells, and cells in the nervous system and the kidney. Production of EGF is induced by testosterone and inhibited by estrogens. EGF stimulates the proliferation and differentiation of mesenchymal cells, acts as a mitogen for fibroblasts, epithelial and endothelial cells, and promotes colony formation of epidermal cells.