Adenosine
In plain terms
A signaling molecule your body already makes, used in skincare as a well-tolerated anti-aging active that helps smooth fine lines and calm skin. It is one of the gentler actives.
What the evidence shows
Adenosine is a small signaling molecule found in every cell of the body, where it helps cells manage energy and communicate. Applied to skin it acts as a mild anti-aging active: controlled studies using precise surface-mapping found that adenosine creams reduced the depth of fine lines around the eyes and forehead over a couple of months, with no adverse effects reported. Its safety profile is reassuring and well characterized. The US cosmetic-ingredient panel judged adenosine safe as used, clearing it up to around one percent in leave-on products, and it did not cause sensitization in the standard maximization test. Because the body makes and clears it constantly, there is no accumulation, hormone, or cancer concern attached to topical use, and it suits sensitive skin. In South Korea it is one of the officially recognized anti-wrinkle actives, which is why it turns up in so many eye and firming creams.
On the label
Listed as adenosine, usually in the active part of an eye cream or anti-aging serum. It is a gentle active, so it layers well and rarely needs the slow introduction that stronger anti-agers like retinoids do.