Generally speaking, retinoids increase the skins sensitivity to sunlight and are therefore recommended for use at night. Tretinoin is the least expensive of the topical retinoids and is the most irritating to the skin, whereas adapalene is the least irritating but costs significantly more. Most formulations of tretinoin are incompatible for use with benzoyl peroxide. Tazarotene is the most effective and expensive topical retinoid but is usually not as well tolerated. In 2019 a tazarotene lotion formulation, marketed to be a less irritating option, was approved by the FDA. Retinol is a form of vitamin A that has similar but milder effects and is present in many over-the-counter moisturizers and other topical products. Isotretinoin is an oral retinoid that is very effective for severe nodular acne, and moderate acne that is stubborn to other treatments. One to two months of use is typically adequate to see improvement. Acne often resolves completely or is much milder after a 4–6 month course of oral isotretinoin. After a single round of treatment, about 80% of people report an improvement, with more than 50% reporting complete remission. About 20% of people require a second course, but 80% of those report improvement, resulting in a cumulative 96% efficacy rate.There are concerns that isotretinoin is linked to adverse effects, like depression, suicidality, and anemia. There is no clear evidence to support some of these claims. Isotretinoin has been found in some studies to be superior to antibiotics or placebo in reducing acne lesions.
Other animals
Acne can occur on cats, dogs, and horses. References
Further reading
External links

Acne Support. Expert, impartial advice on acne by the BAD. "Acne". MedlinePlus. U.S. National Library of Medicine.