What's the difference between a pilonidal and a sebaceous cyst?

Big difference: A sebaceous cyst may occur anywhere sebaceous glands (skin oil glands) are located. These cysts have a lining that sheds cells into the central cavity producing a cheese like appearing white material. A pilonidal cyst occurs in a specific location (near your tailbone) and may be filled with a variety of structures that derive from outer layer of the skin (ectoderm): hair, sebaceous, teeth, etc.

Differences: A pilonidal cyst generally occurs in hairy areas and occurs due to ingrowth of the hairs. A sebaceous cyst occurs when a sebaceous gland becomes blocked and sebaceous material secreted builds up under the skin. Both conditions generally require surgical excision.