Human Defensin β1 (DEFB1), also known as Human Beta-Defensin 1 (hBD-1), is an antimicrobial peptide belonging to the β-defensin family, which also includes DEFB4 (hBD-2) and DEFB103 (hBD-3) that contribute to innate immune defense at epithelial surfaces. In humans (Homo sapiens), DEFB1 is constitutively expressed by epithelial cells in tissues such as the skin, respiratory tract, gastrointestinal tract, and urogenital tract, where it functions as a first-line defense against microbial pathogens. Structurally, DEFB1 is a cationic, cysteine-rich peptide stabilized by disulfide bonds, enabling it to interact with and disrupt microbial membranes, particularly those of bacteria, fungi, and some viruses. In addition to its direct antimicrobial activity, human β-defensin 1 can help regulate immune signaling and leukocyte recruitment, contributing to the maintenance of mucosal immunity and barrier integrity. Dysregulation of DEFB1 expression has been associated with susceptibility to infections, inflammatory diseases, and cancer, particularly in epithelial tissues. Because defensins play key roles in host–microbe interactions and epithelial immune defense, human DEFB1 is widely studied in immunology, infectious disease research, and mucosal biology as an important component of the innate immune system.