Pilosebaceous units are the combination of the hair follicles and oil glands in the skin. Except for the surface of the palms and the soles of the feet, pilosabaceous units are found on the skin tissue throughout the body . They are responsible in secreting the oily substance called sebum. However, due to many factors (e.g. hormonal imbalances, stress and the skin's natural condition) the oil glands may be induced to produce more sebum than normal. When this happens, the excess oil plugs the skin pores. This process brings about bacterial infection and stimulate the reaction of the immune system. In the end, acne inflammation results.