Many people often call any small, painless lump under the skin "sebaceous cysts." But those are most often "epidermoid cysts." Sebaceous cysts are much less common and affect the sebaceous glands, the oil glands in the skin.
Epidermoid cysts can be made up of a protein called keratin and fat. They usually appear on the face, neck, or upper body, especially the chest and shoulders. They erupt for many reasons, most often because of acne or mild skin injuries. (When they are formed because of swelling around hair follicles, they are called pilar cysts.) Epidermoid cysts are usually small, from a few millimeters to about 5 centimeters across, and they grow slowly. They are more common in men than in women.
The cyst itself usually doesn't hurt, but it can become tender, sore, and red if it gets infected. If it pops, the cyst might ooze and smell bad.
Is it dangerous?
No. Epidermoid cysts are harmless and are almost never linked with cancer. If you're worried that it will grow into something more dangerous, check with your doctor to make sure it's not another type of skin problem.
Do I have to have it removed?
Not always. Sometimes, smaller epidermoid cysts go away on their own, or can be treated with warm compresses. Even if a cyst gets infected, a doctor (usually a dermatologist) can sometimes treat it by injecting it with steroids. But if a cyst bothers you for any reason, you can see a doctor to have it removed.
How is an epidermoid cyst removed?
Your doctor may use antibiotics to reduce swelling. Then, after the swelling has eased, he can remove it.
Getting an epidermoid cyst removed is simple. Your doctor will probably numb your skin with local anesthesia, then make a very small cut in the surface of the cyst. He applies firm pressure to squeeze out all of the contents of the cyst or uses a scissors to cut around the cyst to remove the entire sac wall. Be forewarned: Some of that bad-smelling pus inside the cyst may splatter around as it’s draining.