A pilonidal cyst, sometimes called pilonidal disease, is a fluid-filled sac that usually occurs on the tailbone at the top of the buttocks. It usually starts as an infection of a hair follicle in the ...

Also known as a pilonidal cyst, the condition forms when a sac of tissue fills with air or fluid in the crease of your buttocks. Pilonidal cyst, doctors say, is mostly caused by a skin infection.

Dear Dr. Roach • I am writing because my son had a pilonidal cyst removed in March of 2010, almost three years ago. For the first six months, I kept the area clean and free of hair. After six months ...