Retinoids- refers to a family of naturally occurring derivatives of beta-carotene, including Vitamin A, as well as a new class of synthetically produced compounds that are used in prescription products. This class of chemical compounds all have the capability to enhance repair processes in the skin as well as encourage collagen synthesis, cause unplugging of the sebaceous follicle as well as reduce sebum secretion, and affect overall skin metabolism.  For these reasons, retinoids have been widely used for many different dermatologic conditions including anti-aging, acne treatment, lightening, and even for psoriasis.  There are many different retinoids which all produce similar results, but have their own unique qualities as well.  Most of the naturally occurring compounds can be converted into each other through enzymatic pathways in the skin.  Retinols are actually turned into retinoic acid (the main retinoid and considered the active compound in cellular changes).  It has become more common to use retinol (Vitamin A) to treat many skin conditions because it is less drying and irritating, although all of these compounds have this as a potential side effect.  Thus, these are not very good choices for people who have dry or sensitive skin or rosacea.  Also, since they exfoliate the stratum corneum (the dead layer of skin and a barrier to sun as well as water and other irritants), it is critical to use a sunblock and also a moisturizer to counterbalance some of these effects.

Metabolic conversion of retinol in the body follows a complex pathway involving many derivatives. Some of the retinol is converted into retinyl palmitate, considered the storage form of retinol.  The other amount of retinol is first converted to the aldehyde form, retinaldehyde*, in a rate-limiting, reversible step. This process is begun when free retinol associates with a specific cytoplasmic retinol- binding protein {CRBP}.  Retinaldehyde then quickly oxidizes to retinoic acid by retinaldehyde oxidase.  As soon as it is converted, the retinoic acid regulates gene expression profiles through the skin for keratinocyte growth.  The enzyme that turns retinol into retinaldehyde has its activity reduced if there is enough retinoid in the cell (biofeedback control).  Retinoic acid can be further converted into 13-cis retinoic acid or 9-cis retinoic acid.