Photoaggravation of Hair Aging

The document discussed how photoaggravation contributed to hair aging by causing chemical and physical changes in hair fibers, such as increased porosity, loss of mechanical strength, and surface roughness. These changes were due to lipid oxidation, disulfide bond cleavage, tryptophan degradation, and cysteic acid formation. Sunlight exposure made hair more brittle, stiffer, and drier, with reduced water absorption. Hair pigments protected hair proteins by absorbing radiation and dissipating it as heat, but this led to pigment degradation. Dark hair was more resistant to photodegradation than light hair due to the higher photostability of eumelanin. Ultraviolet and visible light degraded hair's integral lipids, weakening the cell membrane complex.