A pilonidal cyst is a raised skin bump filled with stray hair, dead skin or other tissue. It typically occurs between the top of the buttocks near the end of the tailbone, reports the University of Michigan Department of Surgery.
A pilonidal cyst first appears as a small skin indentation and may not even be noticeable, states the Mayo Clinic. The cyst will swell, leak blood or pus and be painful if it becomes infected.
When stray hairs are forcibly pressed down into the skin, the body may view the hair as an unknown substance and develops a cyst to isolate it. Skin chafing, tight clothing or prolonged sitting can cause hair to dig into the skin.
Pilonidal cysts form most often in teenagers and people in their twenties. The condition seldom occurs after age 30, reports the University of Michigan Department of Surgery.
Antibiotic medications are prescribed to treat infected pilonidal cysts and a doctor will remove any blood or pus. If the cysts continue to come back, they can be surgically removed.
If a pilonidal cyst infection is not permanently treated, a person is more likely to get squamous cell carcinoma, a form of skin cancer, states the Mayo Clinic.