Does retinol cause photosensitivity?

We refer to photosensitivity when electromagnetic radiations (UV, visible light, infrared) can trigger skin reactions, such as sunburns. This phenomenon manifests in two forms.

• Photoallergy: less common, it clinically refers to pruritic and erythematous eruptions on skin areas exposed to the sun. These can be immediate or delayed by several days. Photoallergic reactions are due to an immunological hypersensitivity response.

• Phototoxicity: More common, phototoxic reactions, which are non-immunological, are characterised by a skin response resembling an exaggerated sunburn, which occurs a few minutes or even a few hours after exposure to the sun. They are produced following the activation of the photosensitising substance by UV light.

Many medications (tetracyclines, hydrochlorothiazide, sulphonamides, psoralen, etc.) are implicated in photosensitivity reactions. They induce molecular changes in the skin when it is exposed to UV light, making it more photosensitive, or reactive to sunlight or artificial sources.

Topically administered retinoids, including retinol, are believed to be photoreactive molecules. Indeed, the labelling of skincare products and retinoid-based medications suggest or assert that they can increase skin sensitivity upon exposure to UV rays and induce photodermatoses. Numerous studies have been conducted on the photosensitising potential of retinoids with mixed results, particularly on tretinoin, adapalene, tazarotene, or trifarotene. However, there are few studies to date on photosensitivity to retinol. The data seems to show that prescription retinoids, such as tretinoin, adapalene, and tazarotene, do not cause photosensitivity. However, without definitive research, we cannot provide a conclusive answer.

• Adapalene: Adapalene formulations at 0.1 and 0.3%, in cream and gel forms, are used for the treatment of acne. Available studies have not demonstrated that adapalene causes an increased risk of sunburn, and therefore induces phototoxicity or photoallergy in trials. There are no reports on photosensitivity to adapalene in the literature.

• Tazarotene: Tazarotene is a third-generation topical retinoid, commonly used to treat mild to moderate acne and plaque psoriasis. Tazarotene gel is often used in conjunction with narrow-band UVB phototherapy for the treatment of psoriasis. Although no photosensitivity was observed during the three months of treatment with tazarotene gel, anecdotal cases of burning have been reported when the gel was added to the routine of psoriasis patients irradiated with UVB. A study showed that a thick application of tazarotene gel slightly increased the erythemogenicity of UVB, meaning it can make the skin more sensitive to the sun when exposed to it, while a thin application of the gel immediately before phototherapy did not have an erythemogenic effect.

• Tretinoid: A study has shown that the application of trans-retinoic acid (Tretinoin 0.05%) twice a day for 10 days did not produce erythema under UVB exposure. Another combined report from four clinical trials also demonstrated that 0.05% tretinoin gel is neither phototoxic nor photoallergic after 24 hours or 3 weeks of treatment. Further studies have assessed the phototoxicity and photoallergenicity of tretinoin in solution, cream, and gel forms, but the majority have concluded that it is not a phototoxin or a photoallergen. Tretinoin is an irritant and patients who expose their inflamed skin to the sun or wind will exacerbate this discomfort.

According to recent studies, retinoids may not be photosensitising agents in themselves. The erythematous reaction we observe upon sun exposure, following the use of certain topical derivatives of vitamin A, may in fact turn out to be a local irritation of the skin, that is to say, redness, a sensation of heat, itching and some peeling that occur during the first two to four weeks of retinoid use and generally fade with continued application of the treatment.

The typical side effects of retinoids quite clearly coincide with those of a "sunburn". This is probably why labelling guidelines, manufacturers, dermatologists, and skincare experts continue to advise retinoid users to avoid direct UV exposure when using them. It's worth noting that studies show that the increased susceptibility to sunburn generally decreases after the first month of use, which more or less corresponds to the timing of a reaction to retinoids.

The FDA regards isotretinoin (Accutane or Roaccutane), an oral form of Vitamin A used to treat severe acne, as photosensitising. Therefore, it is advised that patients limit their exposure to the sun while taking the medication.

Why is it then preferable to use retinol in the evening ?

This myth surrounding retinol is based on a misunderstanding of its photobiology. With multiple conjugated double bonds, retinoids are likely to undergo a series of photochemical reactions (isomerisation, dimerisation and oxidation). Thus, when exposed to sunlight, the retinol present on the skin's surface can transform into different reactive intermediates. However, these can cause damage to the skin and make the skin sensitive to the sun. That's why it's recommended to use retinol preferably at night, although some formulas can be applied during the day, to address this issue.