Does Vitamin C cause photosensitivity?

A rumour is circulating about the vitamin C (L-ascorbic acid). It is often said to be "photosensitising" and therefore incompatible with sun exposure. This implies that it could make the skin more vulnerable to the harmful effects of the sun's UV rays than usual. Contrary to popular belief, this is simply not true. Vitamin C does not contribute to increasing the skin's sensitivity to the sun as AHA (glycolic acid, citric acid, etc.) can do.

This myth is based on a misunderstanding. In fact, vitamin C is by nature highly unstable, especially when exposed to UV light, and it degrades through chemical and photochemical oxidation into dehydroascorbic acid and 2,3-diketogulonic acid, which are responsible for the yellow colour. For this reason, most skincare formulas are kept at a pH lower than 3.5, which can potentially make the formula irritating for some, and contain "stabilising" ingredients (vitamin E/α-tocopherol, sunscreens, etc.) or alternatively derivatives of vitamin C which are known to be more stable.

UV light reduces the levels of vitamin C in skin tissues. Therefore, it is recommended to use topical pure vitamin C after exposure to UV light rather than before, or to apply it every eight hours for optimal effects.

Far from it, the vitamin C has photoprotective properties due to its potent antioxidant activity. However, it does not absorb UV rays like sunscreens do, but instead provides UV protection by neutralising reactive oxygen species that increase with UV light and other environmental factors (pollution, cigarette smoke, etc.). Indeed, vitamin C helps to limit the acute and chronic photodamage that can be caused by free radicals to the skin by providing these unstable and highly reactive atoms with their missing parts, namely electrons.

Vitamin C cannot replace and does not act as a sunscreen, but it adds an additional layer of protection.