Is it a boil or a cyst, and how do I treat it?

A skin cyst is a sac that forms under the skin and is not painful. Skin cysts do not need to be treated unless they are unsightly or become infected.

A boil is an infection under your skin caused by skin bacteria. A boil usually starts near a hair follicle and becomes painful as pus fills the boil. Boils often need to be drained.

Skin cysts

The most common type of cyst in the skin is an epidermal inclusion cyst. Other names for this cyst are:

• Epidermal cyst
• Infundibular cyst
• Keratin cyst

These cysts are formed when skin cells get trapped under your skin and form a sac that fills with a cheesy-like substance produced by skin cells called keratin.

A less common type of skin cyst is a sebaceous cyst. This skin cyst forms in a blocked skin gland, and it fills with a skin-lubricating substance called sebum.

A skin cyst can occur anywhere on your body. It feels like a firm and painless lump that moves under the surface of your skin when you touch it. There may be a tiny central opening, called a punctum, in the center of the lump. Cysts can range in size from very tiny to a few inches across. Some cysts form and stay about the same size, and some gradually get larger. They may also go away or come back. These cysts are not cancer, and they are not contagious. In rare cases, a person may inherit a disease that causes many cysts called Gardner syndrome.

Cysts are more common in men than women and most common in people between the ages of 20 and 40. They often occur in areas where hair grows. People with acne have a higher risk of cysts. The most common areas for skin cysts to form are on the face, neck, scalp and back.

How to treat skin cysts

A skin cyst is usually diagnosed by the way it looks and feels. It is usually unnecessary to do any diagnostic tests. A skin cyst that is not large and does not show does not need to be treated. A skin cyst that is unsightly or large can be surgically removed. You should never try to treat a skin cyst on your own by squeezing or picking at it. This can cause the cyst to become infected.

Complete surgical removal is the most reliable treatment. It is usually done by a surgical dermatologist as outpatient surgery. The skin is numbed with an anesthetic and opened enough to remove the entire cyst. The opening is then closed with a suture or tape. Other treatment options include injecting the cyst or squeezing it out through a small incision, but these methods have a higher rate of recurrence, which means the cyst may come back.

Infected skin cysts

Some skin cysts may become infected, especially if the cyst is squeezed or bumped. An infected cyst increases in size quickly and becomes painful. It may cause the skin to be warm and red. An infected cyst should be treated. The usual treatment is called incision and drainage. The area over the cyst is numbed and the cyst is opened and drained of pus and keratin.
The cause of the infection is usually a skin bacteria called Staph aureus. Your health care provider may treat you with an antibiotic for Staph aureus if you have fever or the infection has spread outside the cyst. After the cyst has healed, you may need to go back and have it removed by a surgeon, otherwise it is likely to reform and become reinfected.

Boils

A boil is already an infection when it forms under your skin. The infection usually comes from the same skin bacteria that infects cysts, Staph aureus. You can think of a boil as a big, pus-filled pimple. The medical term for a boil is furuncle. When several boils form and come together, it is called a carbuncle. These infections may also be called a skin abscess.

Boils occur when skin bacteria get into a hair follicle and cause a pus-producing infection.

Like skin cysts, boils can be diagnosed by how they look and feel. Unlike cysts, they are tender to touch and become more red and painful as they enlarge. Boils can form anywhere there are hair follicles. They are common in areas that are moist and sweaty, such as the buttocks or armpits. Boils on the face near the nose or eyes are the most dangerous because the infection can spread to the eyes or brain. People who have a weak immune system are more likely to get boils.

How to treat boils

Boils, like pimples, often come to a head and drain on their own. You should never squeeze a boil or try to pick it open. You may be able to help a boil drain by using a warm, moist compress every few hours, like a clean towel soaked in warm water.

A boil that doesn’t drain on its own or becomes painful may need treatment.

The treatment for a boil is incision and drainage of the pus or abscess. Like an infected cyst, the skin is numbed with an anesthetic, and the area over the boil is opened to drain the pus. The opened area may be washed out with sterile salt water during the procedure. Unlike removing a cyst, the skin is left open to allow the boil to drain. In some cases, a small packing is placed into the opened area if it is deep.

Antibiotics against Staph aureus bacteria are used if the boil causes skin redness or fever. Boils have the potential to spread into the bloodstream, called sepsis. Large boils, boils near the center of the face or boils that show signs of sepsis may require admission to the hospital for intravenous antibiotics.