Acne signs and symptoms vary depending on the severity of your condition:

• Whiteheads (closed plugged pores)
• Blackheads (open plugged pores)
• Small red, tender bumps (papules)
• Pimples (pustules), which are papules with pus at their tips
• Large, solid, painful lumps beneath the surface of the skin (nodules)
• Painful, pus-filled lumps beneath the surface of the skin (cystic lesions)

Four main factors cause acne:

• Excess oil production
• Hair follicles clogged by oil and dead skin cells
• Bacteria
• Excess activity of a type of hormone (androgens)

Acne typically appears on your face, forehead, chest, upper back and shoulders because these areas of skin have the most oil (sebaceous) glands. Hair follicles are connected to oil glands.

The follicle wall may bulge and produce a whitehead. Or the plug may be open to the surface and darken, causing a blackhead. A blackhead may look like dirt stuck in pores. But actually the pore is congested with bacteria and oil, which turns brown when it's exposed to the air.

Pimples are raised red spots with a white center that develop when blocked hair follicles become inflamed or infected with bacteria. Blockages and inflammation that develop deep inside hair follicles produce cystlike lumps beneath the surface of your skin. Other pores in your skin, which are the openings of the sweat glands, aren't usually involved in acne.

Factors that may worsen acne

These factors can trigger or aggravate acne:

• Hormones. Androgens are hormones that increase in boys and girls during puberty and cause the sebaceous glands to enlarge and make more sebum. Hormonal changes related to pregnancy and the use of oral contraceptives also can affect sebum production. And low amounts of androgens circulate in the blood of women and can worsen acne.
• Certain medications. Examples include drugs containing corticosteroids, testosterone or lithium.
• Diet. Studies indicate that certain dietary factors, including skim milk and carbohydrate-rich foods — such as bread, bagels and chips — may worsen acne. Chocolate has long been suspected of making acne worse. A small study of 14 men with acne showed that eating chocolate was related to a worsening of symptoms. Further study is needed to examine why this happens and whether people with acne would benefit from following specific dietary restrictions.
• Stress. Stress can make acne worse.

Acne myths

These factors have little effect on acne:

• Greasy foods. Eating greasy food has little to no effect on acne. Though working in a greasy area, such as a kitchen with fry vats, does because the oil can stick to the skin and block the hair follicles. This further irritates the skin or promotes acne.
• Hygiene. Acne isn't caused by dirty skin. In fact, scrubbing the skin too hard or cleansing with harsh soaps or chemicals irritates the skin and can make acne worse.
• Cosmetics. Cosmetics don't necessarily worsen acne, especially if you use oil-free makeup that doesn't clog pores (noncomedogenics) and remove makeup regularly. Nonoily cosmetics don't interfere with the effectiveness of acne drugs.

Risk factors for acne include:

• Age. People of all ages can get acne, but it's most common in teenagers.
• Hormonal changes. Such changes are common in teenagers, women and girls, and people using certain medications, including those containing corticosteroids, androgens or lithium.
• Family history. Genetics plays a role in acne. If both parents had acne, you're likely to develop it, too.
• Greasy or oily substances. You may develop acne where your skin comes into contact with oily lotions and creams or with grease in a work area, such as a kitchen with fry vats.
• Friction or pressure on your skin. This can be caused by items such as telephones, cellphones, helmets, tight collars and backpacks.
• Stress. Stress doesn't cause acne, but if you have acne already, it may make it worse.