Tretinoin: What is it?

If you’ve ever wondered about the connection between tretinoin, vitamin A, and retinol, you’re in the right place. In this post, we explain where tretinoin comes from and its relationship to Vitamin A, retinols, and retinoids.

Understanding Vitamin A and Its Derivatives

Tretinoin is a derivate (metabolic product) of Vitamin A. We get vitamin A from our diet in the form of retinyl esters and provitamin A carotenoids (with beta-carotene being especially efficient). In the intestine, it's converted to retinol, which is absorbed and then stored in the liver. When needed, the liver releases retinol into the bloodstream and it is transported to tissues were it is taken up by cells.

Once inside cells, retinol is converted to retinaldehyde (aka retinal), an intermediate product, then into retinoic acid, primarily the all-trans form also known as tretinoin. This is the active form of vitamin A that binds receptors inside cells inducing its effects.

To summarize important terms:

• Vitamin A: a broad term used to refer to a number of different molecules very closely related to vitamin A in structure including: provitamins of vitamin A like that beta-carotene, alpha-carotene, and beta-cryptoxanthin, vitamin A esters and alcohols like retinyl palmitate or retinyl acetate, and retinol.

• Retinol: often found in over-the-counter skincare products, retinol is the alcohol form of vitamin A. When applied to the skin, retinol must undergo a transformation into retinoic acid (mainly tretinoin) to exert its beneficial effects.

• Retinaldehyde (retinal): This is an intermediate product in the conversion process and is less commonly used in skincare products.

• Retinoic Acids: A family of isomers (compounds with the same ingredients but different structural arrangements) including primarily all-trans retinoic acid (tretinoin), along with small amounts of 13‑cis retinoic acid (isotretinoin, aka Accutane), and even less of 9‑cis retinoic acid.

Retinoids: Compounds Derived from Vitamin A

Retinoid is a broad term used for the the class of compounds that are derived from vitamin A. Tretinoin is one, but there are many others encompassing both substances produced naturally in our skin and those produced synthetically in a lab by chemists.

• Natural Retinoids: including retinol, retinal, tretinoin, isotretinoin, and alitretinoin are vital for various biological processes including vision, immune function, skin health, and fetal development.

• Synthetic Retinoids: including adapalene, tazarotene, trifarotene, acitretin, and bexaroten do not occur naturally in our body's biochemical processes but are components of multiple prescription skin care treatments.

Retinoids vary widely in their spectrum of activity, toxicity, and clinical applications. They work inside our cells by binding to specialized proteins known as receptors—specifically, RARs and RXRs—which act like switches to turn genes on or off. These receptors are present in varying amounts in different cell types and can combine in multiple ways, sometimes pairing with one another or with other receptor types, to regulate a wide array of genes. Moreover, each retinoid tends to bind selectively to certain receptors, forming complexes that can either boost or slow down gene activity. As a result, different retinoids can produce markedly different effects on the skin.

More to Come

Over the next couple of weeks we will be exploring different myths and truths about tretinoin in a variety of social media and blog posts. So, stay tuned and follow me on Instagram to stay up to date.

Dr. Ryan M. Trowbridge, MD, MS, MA

Harvard-Trained Board-Certified Dermatologist and DermMythBuster