Hidradenitis suppurativa can affect one spot or multiple areas of the body. Signs and symptoms of the condition include:

• Blackheads. Small pitted areas of skin containing blackheads — often appearing in pairs or a "double-barreled" pattern — are a common feature.
• Painful pea-sized lumps. The condition usually starts with a single, painful lump under the skin that persists for weeks or months. Later more bumps form. They usually appear in areas with hair follicles with many oil and sweat glands, such as the armpits, groin and anal area. They also occur where skin rubs together, such as the inner thighs, breast and buttocks.
• Tunnels. Over time, tracts connecting the lumps may form under the skin. These wounds heal very slowly, if at all, and can leak pus, which may have an odor.

Some people with this condition experience only mild symptoms. Excess weight, stress, hormonal changes, heat or humidity may worsen symptoms. In women, the disease severity may lessen after menopause.

The exact cause of hidradenitis suppurativa isn't known. It develops when hair follicles in the skin become blocked. Experts think it could be connected to hormones, inherited genes and immune system problems. Smoking, excess weight and metabolic syndrome also might play a role.

Hidradenitis suppurativa is not caused by an infection or being unclean, and it can't be spread to other people.

Factors that increase your chance of developing hidradenitis suppurativa include:

• Age. Hidradenitis suppurativa most commonly occurs in women between the ages of 18 and 29. People who develop the condition at an early age may be at increased risk of developing more widespread disease.
• Your sex. Women are more likely to develop hidradenitis suppurativa than are men.
• Family history. A tendency to develop hidradenitis suppurativa can be inherited.
• Obesity. Several studies have shown a relationship between being overweight and hidradenitis suppurativa.
• Smoking. Smoking tobacco has been linked to hidradenitis suppurativa.

Persistent and severe hidradenitis suppurativa often causes complications, including:

• Infection. The affected area is susceptible to infection.
• Scars and skin changes. The wounds may heal but leave rope-like scars or pitted skin.
• Restricted movement. Sores and scar tissue may cause limited or painful movement, especially when the disease affects the armpits or thighs.
• Obstructed lymph drainage. The most common sites for hidradenitis suppurativa also contain many lymph nodes. Scar tissue can interfere with the lymph drainage system, which may result in swelling in the arms, legs or genitals.
• Social isolation. The location, drainage and odor of the sores can cause embarrassment and reluctance to go out in public, leading to sadness or depression.