Folic acid (FA) is an essential vitamin; however, when exposed to ultraviolet (UV) radiation, it undergoes photodegradation to form fl uorescent products, specifically 6-carboxypterin and 6-formylpterin. These compounds belong to the class of pterins, which can act as endogenous photosensitizers and accumulate in the skin in certain pathologies. The interaction of these photoproducts with proteins, particularly serum albumin, the main transport protein of blood plasma and interstitial fl uid, determines their biodistribution and photosensitizing activity.
