There are two types of acne lesions: inflammatory and noninflammatory. Inflammatory lesions are inflamed when blood penetrates the follicle after it has ruptured. The two prominent types of inflammatory acne lesions are papules and pustules. Noninflammatory lesions are open and closed comedones that are not red or inflamed.
A comedone consists of a mixture of dead cells and sebum that forms a plug in a sebaceous follicle and evolves from a microcomedone. There are two main types of comedones: open comedones and closed comedones, both categorized as noninflammatory acne lesions because they are not red and inflamed. Open comedones are also known as blackheads—dilated follicles in which oxygen has oxidized the sebum. Closed comedones are commonly known as a whiteheads
