The scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts, though they may occur anywhere on the body except the palms of the hands and soles of the feet. In males a common place for them to develop is the scrotum and chest. They are more common in hairier areas, where in cases of long duration they could result in hair loss on the skin surface immediately above the cyst. They are smooth to the touch, vary in size, and are generally round in shape.
They are generally mobile masses that can consist of:
– Fibrous tissues and fluids
– A fatty (keratinous) substance that resembles cottage cheese, in which case the cyst may be called “keratin cyst” This material has a characteristic “cheesy” or foot odor smell,
– A somewhat viscous, serosanguineous fluid (containing purulent and bloody material).
The nature of the contents of a sebaceous cyst, and of its surrounding capsule, will be determined by whether the cyst has ever been infected.
With surgery, a cyst can usually be excised in its entirety. Poor surgical technique or previous infection leading to scarring and tethering of the cyst to the surrounding tissue may lead to rupture during excision and removal. A completely removed cyst will not recur, though if the patient has a predisposition to cyst formation, further cysts may develop in the same general area.
Blocked sebaceous glands, swollen hair follicles, high levels of testosterone and the use of androgenic anabolic steroids will cause such cysts.
A case has been reported of a sebaceous cyst being caused by the human botfly.
Hereditary causes of sebaceous cysts include Gardner’s syndrome and basal cell nevus syndrome.
About 90% of pilar cysts occur on the scalp, with the remaining sometimes occurring on the face, trunk and extremities. Pilar cysts are significantly more common in females, and a tendency to develop these cysts is often inherited in an autosomal dominant pattern.In most cases, multiple pilar cysts appear at once.