Though the exact cause of acne is unknown, many doctors believe it is a direct result of a variety of factors. One of these factors is the increase in androgens during puberty. Androgens are hormones, and can cause the enlargement and overstimulation of the sebaceous glands in people with acne. For both males and females, the increase in androgens during puberty can cause these sebaceous glands to produce more sebum, which is oil. This oil mixes with dead skin cells and bacteria on the skin and blocks pores. Inside of these blocked pores bacteria multiplies and leads to swelling, which then causes spots and pimples. Some researchers also believe that acne is hereditary, and that people with parents who had acne are likely to inherit acne. Though stress has not been found to be a direct cause of acne, it can lead to aggravated cases of acne. This happens because when someone is laden with anxiety, their body produces hormones such as cortisol, which exacerbates acne. Other possible causes of acne include certain medications, drugs, steroids, have or oily make-up, and harsh skin cleansing. Greasy foods and dirty skin have often been blamed for acne, but there is little evidence supporting these as direct causes of acne. Acne is also not contagious.