Abstract: Peptidyl arginine deiminases (PADIs) are expressed in the hair follicle stem cell lineage and mediate the conversion of arginine to citrulline, affecting the hair follicle cycle. They play a crucial role in the activation, lineage identification, and differentiation of hair follicle stem cells. Citrulline drives pro-inflammatory circuits, neutrophil infiltration, recruitment, and activation of T lymphocytes, leading to hair follicle degeneration and alopecia. Therefore, citrullination has a role in regulating hair follicle regeneration and may cause inflammatory alopecia. This paper reviews the update of the mechanisms of action of PADIs in the hair follicle cycle and inflammatory alopecia.

Key words: peptidyl arginine deiminases, hair follicle cycle, citrullination, inflammatory hair loss