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Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

What Is It?

Acne is a common skin condition. It is caused by inflammation of the hair follicles and oil-producing (sebaceous) glands of the skin.

Hair follicles are the tiny structures that grow hair in the scalp. Sebaceous glands produce sebum. On areas where acne develops, sebaceous glands surround the hair follicles. The combination of the sebaceous glands and the hair follicles is the "pilosebaceous unit," where acne pimples and cysts develop. Sebum moisturizes hair and skin. Each hair pushes up through the skin surface along with sebum.

Acne often begins during puberty. It occurs when sebaceous glands in the skin are over-stimulated to produce sebum and skin cells are not shed normally. These sticky cells block the skin's hair follicles, trapping the sebum.

The blocked, oil-filled follicle then causes the bacteria normally in the hair follicles to multiply. This leads to inflammation, redness and pimples (pustules).

In adolescents, acne flare-ups probably are related to a natural increase in androgen hormones during the teen years. These androgens stimulate the sebaceous glands to produce excess sebum. Hereditary factors also contribute to the problem.

Other factors that can lead to acne include:

  • Oily cosmetics

  • Humidity

  • Heavy sweating

  • Problems with the ovaries or adrenal glands

  • Drugs such as:

    • Lithium

    • Steroids, both prescription steroids and potentially harmful "body-building" steroids

Acne is not related to diet or poor hygiene. In fact, too much washing can cause an acne flare-up to get worse.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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