There are several types of cysts, and each type of cyst has a different cause and symptoms. Cysts usually develop when a hair follicle becomes blocked.
EPIDERMOID (SEBACEOUS) CYSTS
Also known as sebaceous cysts, epidermoid cysts are slow-growing bumps that usually appear on the scalp, face, ears, trunk, back, or groin area. These cysts can develop when something damages or blocks the gland or its duct such as a scratch, a surgical wound, or a skin condition like acne. The cysts are filled with a foul-smelling material, which may occasionally drain. A ruptured epidermoid cyst may become red, inflamed, swollen, and painful.
PILAR CYSTS
Pilar cysts usually develop as the result of damage to the hair follicle. More than 90 percent of pilar cysts appear on the scalp, causing pain and discomfort when the person brushes, combs, or washes their hair.