Two of the most common harmless lumps under the skin are epidermoid cysts and lipomas. They are often confused, but they are made of different things and are treated in different ways.
Epidermoid cyst
An epidermoid cyst is a sac in the skin filled with keratin, a soft, cheesy, white or yellow material. It usually sits close to the surface and feels firm and round. Many have a small dark opening on top (a punctum). It may move a little under the skin but is attached to the skin above it.
These cysts can become inflamed, red, and painful, and they may leak a material with a strong smell. They are common on the face, neck, back, and chest.
Lipoma
A lipoma is a slow-growing lump of fat cells. It sits deeper, under the skin rather than in it. It feels soft and rubbery and usually moves easily when you press it with a finger. Lipomas have no opening on the surface, do not leak, and are usually painless.
They often appear on the shoulders, back, neck, arms, and thighs and can grow quite large over many years.
Quick comparison
Cysts are firmer, closer to the skin, can have a punctum, and can become inflamed. Lipomas are softer, deeper, more mobile, and rarely painful. A doctor can usually tell the difference by examining the lump, sometimes with an ultrasound.
Treatment
Neither needs treatment if it is small and does not bother you. Cysts are removed by cutting out the whole sac, otherwise they return. Lipomas are removed through a small incision, and the fatty lump often comes out in one piece.
Any lump that grows quickly, feels hard and fixed, or causes pain should be checked by a doctor. The videos below show professional skin treatments in detail.
