According to Dr. Francesca Fusco, Assistant Clinical Professor of Dermatology at Mount Sinai, in the article, "Maybe Self-Tanners Aren't So Great After All", DHA may stain pores, and "the usual cause of their dark appearance is due to free radicals, which are unstable atoms in the skin linked to acne and visible signs of aging". The article then goes on to explain how if one regularly uses self tanner, oxidation on the surface of your skin increases by nearly double. Therefore, this effect could be comparable to the negative implications of excessive sun exposure. However, what the above claim did not mention is that the study finding these oxidation levels was conducted with a solution of 20% DHA, which is highly uncommon. Most self-tanning products only include one to two percent DHA, proving the above claim to be misleading.
According to Sarah Beer, M.D., in the Piedmont Healthcare article titled, "Is self-tanner safer than the sun?", sunless tanners are a safer option than exposing your skin to the sun because the self-tanners "tint the top layer of the skin that sloughs off in two to three weeks" as opposed to UV rays from the sun which could cause "cellular changes that can turn malignant or cancerous". Additionally, it is explained that DHA is deemed safe because it is plant derived and approved by the FDA for skin tanning. Although self-tanner might cause temporary changes to the skin, it is exaggerative to claim that it is just as unsafe or more unsafe than radiation from the actual sun.
https://intothegloss.com/2019/08/self-tanners-and-skincare/
https://www.piedmont.org/living-real-change/is-self-tanner-safer-than-the-sun#:~:text=She%20adds%20that%20sunless%20tanners,(FDA)%20for%20skin%20tanning.