Retinoids are derivatives of vitamin A. There are synthetic and naturally occurring retinoids and they are available for oral and topical use. Retinoids are used in a variety of products available over-the-counter and by prescription. They work by binding to specific receptors which then interact with DNA. This process generates new molecules which in turn results in skin improvements. The most common topical skin retinoids are tretinoin, tazarotene and adapalene, with tretinoin and tazarotene used most frequently to treat photoaging.