The development of acne has several causes. Hormonal changes in puberty cause the skin to change and the sebaceous glands to produce more sebum. Sebum, skin flakes and bacteria can eventually cause a blockage and inflammation of the sebaceous glands. Often acne vulgaris can be mild in nature. If the acne is characterised mainly by blackheads, it may be a case of acne comedonica. If there are frequent and large inflammations present, an acne vulgaris can pass into an acne conglobata.