There are many myths about what causes acne. Chocolate and greasy foods are often blamed, but there is little evidence that foods have much effect on the development and course of acne in most people. Another common myth is that dirty skin causes acne; however, blackheads and other acne lesions are not caused by dirt. Stress doesn’t cause acne, but research suggests that for people who have acne, stress can make it worse.
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Factors That Can Make Acne Worse
Factors that can cause an acne flare include:
- Changing hormone levels in adolescent girls and adult women 2 to 7 days before their menstrual period starts
- Oil from skin products (moisturizers or cosmetics) or grease encountered in the work environment (for example, a kitchen with fry vats)
- Pressure from sports helmets or equipment, backpacks, tight collars, or tight sports uniforms
- Environmental irritants, such as pollution and high humidity
- Squeezing or picking at blemishes
- Hard scrubbing of the skin
- Stress.
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How Does Acne Develop?
Doctors describe acne as a disease of the pilosebaceous units (PSUs). Found over most of the body, PSUs consist of a sebaceous gland connected to a canal, called a follicle, that contains a fine hair (see “Normal Pilosebaceous Unit” diagram). These units are most numerous on the face, upper back, and chest. The sebaceous glands make an oily substance called sebum that normally empties onto the skin surface through the opening of the follicle, commonly called a pore. Cells called keratinocytes line the follicle.
Normal Pilosebaceous Unit

The hair, sebum, and keratinocytes that fill the narrow follicle may produce a plug, which is an early sign of acne. The plug prevents sebum from reaching the surface of the skin through a pore. The mixture of oil and cells allows bacteria Propionibacterium acnes (P. acnes) that normally live on the skin to grow in the plugged follicles. These bacteria produce chemicals and enzymes and attract white blood cells that cause inflammation. (Inflammation is a characteristic reaction of tissues to disease or injury and is marked by four signs: swelling, redness, heat, and pain.) When the wall of the plugged follicle breaks down, it spills everything into the nearby skin – sebum, shed skin cells, and bacteria – leading to lesions or pimples.
People with acne frequently have a variety of lesions, some of which are shown in the diagrams below. The basic acne lesion, called the comedo (KOM-e-do), is simply an enlarged and plugged hair follicle. If the plugged follicle, or comedo, stays beneath the skin, it is called a closed comedo and produces a white bump called a whitehead. A comedo that reaches the surface of the skin and opens up is called an open comedo or blackhead because it looks black on the skin’s surface. This black discoloration is due to changes in sebum as it is exposed to air. It is not due to dirt. Both whiteheads and blackheads may stay in the skin for a long time.
Types of Lesions

Other troublesome acne lesions can develop, including the following:
- Papules – inflamed lesions that usually appear as small, pink bumps on the skin and can be tender to the touch
- Pustules (pimples) – papules topped by white or yellow pus-filled lesions that may be red at the base
- Nodules – large, painful, solid lesions that are lodged deep within the skin
- Cysts – deep, painful, pus-filled lesions that can cause scarring.
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What Is Acne?
Acne is a disorder resulting from the action of hormones and other substances on the skin’s oil glands (sebaceous glands) and hair follicles. These factors lead to plugged pores and outbreaks of lesions commonly called pimples or zits. Acne lesions usually occur on the face, neck, back, chest, and shoulders. Although acne is usually not a serious health threat, it can be a source of significant emotional distress. Severe acne can lead to permanent scarring.
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