What it is
Adenosine is a nucleoside (molecular formula C10H13N5O4) made of the purine base adenine joined to the sugar ribose through a beta-N9-glycosidic bond. In the body it is one of the building blocks of RNA and the backbone of the energy carriers AMP, ADP, and ATP, and it acts as a signaling molecule through dedicated adenosine receptors. In skincare it is used as a cell-communicating, skin-conditioning ingredient associated with a soothing, smoothing effect, which is why it is common in calming and barrier-support formulas including many sunscreens.
Safety & warnings
Adenosine is an endogenous molecule that the skin already contains, and it is generally considered gentle and well tolerated even in leave-on products and around delicate areas. It is not a known sensitizer or common allergen, and is widely used in formulas aimed at sensitive or reactive skin. As with any active, anyone with a known reaction to a specific product should patch test first.