Topical, prescription-only medication that can improve skin cell maturation after skin has been damaged. It is the active ingredient in Retin-A, Renova, Tazorac, and Avita (and also available as a generic). Tretinoin is prescribed in various strengths and bases (cream, lotion) depending on the person’s skin type and concerns.
One of the more significant problems of sun damage is abnormal and mutated cell growth. Because there are receptor sites on skin cells for tretinoin, this ingredient can attach to those sites as they migrate through the skin and “tell” the cell to start behaving normally. Tretinoin cannot undo the cell mutations sun damage causes, but it can help the damaged cells behave more like they did before they became damaged.
An article in Clinics in Geriatric Medicine (November 2001, pages 643–659) stated that “Studies that have elucidated photoaging pathophysiology have produced significant evidence that topical tretinoin (all-trans retinoic acid), the only agent approved so far for the treatment of photoaging, also works to prevent it” (Sources: Cosmetic Dermatology, December 2001, page 38; and Journal of Investigative Dermatology, 2001, volume 111, pages 778–784).
Tretinoin affects and improves actual cell production deep in the dermis, far away from the surface of skin (Sources: Clinical and Experimental Dermatology, October 2001, pages 613–618; Clinics in Geriatric Medicine, November 2001, pages 643–659; and Photochemistry and Photobiology, February 1999, pages 154–157). No one is 100% sure how it works, but we know to some extent it modifies how new skin cells are formed, shaped, and mature, which in turn affects how these cells look and act when they reach skin’s surface.
A common misconception is that tretinoin exfoliates skin like an AHA (alpha hydroxy acid) or BHA (beta hydroxy acid) product. However, tretinoin is not an exfoliant. Tretinoin improves living cells so they can shed normally whereas AHA and BHA exfoliants dissolve dead skin cells in skin’s uppermost layers. Tretinoin improves how skin cells shed naturally, helping them do so in the manner they did before being damaged by sun exposure. But this action is not the same as exfoliation. It gets confusing because tretinoin does affect how skin cells form and shed deeper in the skin, beyond where AHAs and BHA ingredients reach. But technically what’s going in terms of how skin cells shed isn’t the same action as exfoliating skin’s surface to improve its appearance.
It is perfectly OK (and for many, quite beneficial) to combine tretinoin with an AHA or BHA exfoliant. Which one to apply first is a matter of personal preference and experimentation.