Acne gives the combination of symptoms like greasy skin, white heads, black heads, pimples, inflammation and scar formation. Acne mostly affects young people in the age 14 - 25, but also sometimes older persons, like women in their menopause. 

The skin has several layers: The outer layer called epidermis. Under this lies the dermis consisting of connective tissue. At the bottom a layer called the hypodermis consisting of fat cells.

Acne starts by the glands in the hair follicles increasing their sebum production. This will in the beginning only cause greasy skin. Eventually the sebum in the entrance of the follicles mixes with dead epithelial cells. This mix reacts chemically to forms hard props, comedones that close the pore entrances. According to the color of the comedones, they are called black heads or white heads.

Then the closed hair follicle gets filled with sebum and swell. The swollen follicle then gets infected by bacteria. The accumulated sebum and bacteria cause the follicle and the surrounding skin to get inflamed, forming a pimple.  Then the inflamed follicle burst. Eventually the affected area heals. Sometimes the inflammation reaches deep into the skin and destroys skin tissue. This will cause distinct scars which some may be permanent. Typically an affected person will have follicles in all these stages at any given time.