Inside the follicle, the hair extends up from the deep layers of the skin and comes out of a pore. The sebum lubricates the skin and provides a protective barrier to prevent drying. Skin on the face, chest, and back has an especially large number of sebaceous glands. These are the areas where acne occurs. Open and closed comedones along with papules and pustules are referred to as papulopustular acne a form of inflammatory acne.
Nodular acne is the most severe form of inflammatory acne.
Noninflammatory acne Open comedones result from the enlargement and dilation of a plug that forms from oil and flakes of skin inside the hair follicle. The dark color is not dirt inside the pore. Instead it is the oil inside the pore, which has become exposed from the outside air. A closed comedo forms if the hair follicle pore remains closed. The plug in a closed comedo or whitehead is therefore not exposed to the outside air, and no black color develops.