Acne vulgaris is a chronic disease of the pilosebaceous unit.

The primary alteration is desquamation of follicular corneocytes into the sebaceous follicle ducts, forming a plug.

When present for a prolonged period, the plug can be seen clinically as a comedone.

Acne patients tend to have larger sebaceous glands and produce more sebum than do persons without acne. However, patients with very dry skin also may have a great deal of acne activity.

Nevertheless, the free fatty acid portion of sebum may be a contributing cause of inflammation.

The anaerobic diphtheroid Propionibacterium acnes, which is found in hair follicles, is important in inducing inflammation through chemotactic factors and host response.

Androgenic stimulation is important in both men and women because it drives sebaceous gland secretion.

Other hormonal influences also may play a role; women often have exacerbations of acne activity in the perimenstrual period.

Emotional stressors appear to play a role in acute acne exacerbations but not in chronic acne vulgaris.