Azelaic acid is present in our skin naturally: it is produced by normal skin’s microbiome. In skincare, it is an effective and relatively gentle ingredient that helps reduce hyperpigmentation, calm down inflammation and can help neutralize free radicals. It is successfully used for treatment of acne, melasma, and rosacea. It has a mild exfoliating effect. It might also be able to help regulate sebum production in skin and help speed up the skin cell turnover.
Azelaic acid does not absorb UV and visible light, meaning that it is highly unlikely to cause sun sensitivity (in other words, a photoirritative or photosensitive reaction). At the same time, there are rare reports of photosensitivity when using topical medications (creams, gels) with azelaic acid. It is possible that these reactions are caused by other ingredients in the formula.
While azelaic acid is highly unlikely to lead to sun sensitivity, it is still a good idea to be extra cautious when it comes to sun exposure if you are using azelaic acid. The main reason is that if you are using azelaic acid, you are probably concerned with hyperpigmentation and/or acne, blackheads and clogged pores. Sun is not your skin’s friend in these conditions, and you need to limit the UV exposure as much as possible. This is why it is a great idea to wear a broad spectrum sunscreen with high SPF daily, avoid direct sun and wear sun-protective hat and clothing if you are using azelaic acid. If you want to be extra-cautious, you might prefer to use products with azelaic acid at night. It is not strictly necessary, especially if you are not going to spend your day in a direct sunlight, but many people prefer doing it anyway because the texture of products with azelaic acid does not always work great under sunscreens and makeup.
Photo by Daoudi Aissa
Experience of applying azelaic acid in dermatology https://vestnikdv.ru/jour/article/view/251/252
Drug-Induced Photosensitivity https://journals.sagepub.com/doi/abs/10.1310/hpj4102-196
Azelaic Acid: Properties and Mode of Action https://www.karger.com/Article/Abstract/354888