October 2006
Dear Paula,
My question is about retinol. I have read many of the articles you have online and know that Retin-A should not be combined with benzoyl peroxide, and that it makes sense to use one at night and the other in the morning. I have some questions related to that. Does this same directive apply to over-the-counter moisturizers containing retinol or retinyl palmitate? Should retinol products be used at night versus daytime or is that just personal preference? I have heard that it is best to use retinol products at night due to potential sun sensitivity. However, if a proper sunscreen is used, would it matter?

Rebekah, via email 

Dear Rebekah,
Retin-A, a topical prescription medication for acne (and wrinkles), contains tretinoin, a derivative of vitamin A. While it is well-known that tretinoin and benzoyl peroxide should not be mixed because the two aren't compatible (one deactivates the other), there is no information as to how that relates to retinyl palmitate or retinol (retinol is the entire vitamin A molecule and retinyl palmitate is an ester form). Benzoyl peroxide does not affect adapalene, a form of vitamin A found in the prescription medication Differin. To make an educated guess, I would say it probably doesn't matter, assuming it is something unique about tretinoin in relation to benzoyl peroxide that keeps them at odds.

In terms of sun sensitivity, there is nothing about using Retin-A or any form of vitamin A on the skin that makes the skin more photoreactive or phototoxic. Those concerns do apply for isotretinoin, however, which absolutely makes the sun more damaging to skin by causing a potential phototoxic reaction. It is easy to see where the isotretinoin in isotretinoin gets confused with the tretinoin found in Retin-A or Renova. However, what may happen when you first begin to use Retin-A or Renova is that the skin tends to become sensitive and flakes like mad because of the irritation. That can make the skin more sensitive to the sun, but sunscreen should take care of the problem because it isn't a photosensitizing reaction. Once your skin gets used to the tretinoin and the flaking stops, it will still need sunscreen, but it won't be more vulnerable to a sun reaction.