Since their introduction in the 1980s, retinoids have been increasingly used for topical and systemic treatment of skin conditions such as acne-related dermatoses or psoriasis but also for therapy and/or chemoprevention of skin cancer and other neoplasia. Along the years, chemical modifications have led to more efficient and safer drugs. But, from a photobiological viewpoint, development of the 3rd generation of polyaromatic retinoids calls the attention on their potential photoactivity. In this context, adapalene along with tazarotene and tretinoin are currently the three topical retinoids approved so far by the Food and Drug Administration (FDA).
Therefore, a detailed study of their photophysical and photobiological properties is critical to evaluate their photoreactivity toward biological components and their potential use as phototherapeutic agents. In a first stage, the photophysical properties of these drugs are investigated to get more insight into their excited states and their potential to trigger biomolecule damages. Then, retinoids phototoxicity is established in vitro using the standard Balb/c 3T3 NRU assay, that reveals a photoirritation factor (PIF) higher than the threshold of 5 set by the guidelines for phototoxic compounds. The Type II reactivity of these topical drugs is discussed together with their potential activity and use as phototherapeutic agents.