Acne vulgaris, or acne, is a skin disease. It is also called pimple or zit. It is caused by the changes in the hair follicle and the sebaceous gland surrounding it. The sebaceous gland produces sebum, an oily substance that makes the skin and hair waterproof to avoid drying. Excess production of sebum blocks the pores of the skin, then it accumulates inside and naturally occurring bacteria causes inflammation and skin irritation. Blackheads and whiteheads are also pore blockage – blackheads are dark because it is oxidized keratin, while whiteheads are trapped keratin. It is not true that dirt causes acne and blackheads. Rather it is caused by trapped sebum, and ordinary washing of the face cannot remove it.