Definition

A boil is a red, swollen, painful bump under the skin that is caused by an infection. Boils often start in an infected hair follicle. Bacteria form an abscess or pocket of pus. With time, the pus may come to a head and drain out through the skin. Boils can occur anywhere, but common sites include the face, neck, armpits, buttocks, groin, and thighs.

There are several types of boils:

• Furuncle or carbuncle—an abscess caused by the bacteria Staphylococcus aureus or Streptococcus pyogenes, sometimes occurs as several boils in a group
• Pilonidal cyst—an abscess that occurs in the crease of the buttocks and almost always requires medical treatment
• Cystic acne—an abscess that occurs when oil ducts become clogged and infected, more common in the teenage years
• Hidradenitis suppurativa—an uncommon disorder where multiple abscesses occur in the armpit and groin area

Pilonidal Cyst

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Causes

Causes of boils may include:

• Bacteria, including Staphylococcus aureus
• Ingrown hair
• Splinter or foreign object lodged in the skin
• Blocked sweat gland or oil duct

Risk Factors

Factors that increase your risk of getting a boil include:

• Diabetes
• Poor nutrition
• Poor hygiene
• Weakened immune system
• Exposure to harsh chemicals

Symptoms

Symptoms may include:

• Skin lump or bump that is red, swollen, and tender
• Lump that becomes larger, more painful, and softer over time
• A pocket of pus that may form on top of the boil

Diagnosis

The doctor will ask about your symptoms and medical history and perform a physical exam. A bacterial culture of the boil may be taken.

Some boils do not need medical attention and may drain on their own. More serious symptoms from boils may require treatment. These include:

• The boil worsens, continues, or becomes large or severe
• You have a fever
• The skin around the boil turns red or red streaks appear
• The boil does not drain
• An additional boil or boils appear
• The boil limits your normal activities
• The boil is on your face, near your spine, or in the anal area
• You have diabetes
• You develop many boils over several months

Treatment

Your doctor can drain the boil if needed and treat the infection with antibiotics.

Home treatment may include:

Prevention

To help prevent boils:

• Practice good hygiene. Wash boil-prone areas with soap and water or an antibacterial soap. Dry thoroughly.
• Clean and treat any minor skin wounds.
• Avoid clothing that is too tight.