The cause of acne is not well understood. Although stress can cause acne, it is not considered a cause.
Acne mainly affects people in their teens and early twenties. During puberty, both boys and girls produce high levels of androgen, the male sex hormone that includes testosterone. Testosterone signals the body to make more fat in the sebaceous glands.
Excessive fat secretion clogs the pores, especially around the face, neck, chest and back. Bacteria grow in these clogged pores. This causes blackheads or whiteheads on the skin surface.
Type of contraceptive pill can also cause acne in some women. Some other types of injections, and IUDs can also cause acne.
People who have survived adolescence without acne are more likely to develop acne in adulthood or old age. Although an increase in androgen levels in adulthood, some doctors believe that acne is less likely to be related to androgen levels, but it seems to be related to an increase in the production of fat or bacteria that cause acne.