Acne can be caused by a variety of factors, including hormonal changes, genetics, stress, and certain medications. When hormone levels fluctuate, the skin's sebaceous glands produce more oil, which can clog pores and lead to acne. Bacteria on the skin can also contribute to the development of acne by causing inflammation and infection. In addition, lifestyle factors such as diet, sleep, stress and exercise can play a role in the development and severity of acne.