A large, dark lump on the back can understandably look concerning, particularly when the surrounding skin appears red, swollen, or irritated. One possible explanation is an epidermoid cyst, but photographs alone cannot establish a diagnosis. Other skin conditions can produce similar-looking lumps, making an examination by a healthcare professional important.

Epidermoid cysts develop beneath the skin and commonly occur on the trunk. Some have a small opening in the center and can remain relatively harmless for years. However, they may become inflamed, painful, swollen, or rupture. Redness can occur with inflammation and does not necessarily mean that the cyst is infected.

Treatment depends on the size and condition of the lump and whether it is causing symptoms. A healthcare professional may recommend drainage if an inflamed cyst is particularly painful or swollen. In some cases, medication or an injection may help control inflammation. When appropriate, removing the entire cyst can reduce the likelihood of it returning, although removal may sometimes be delayed while severe inflammation settles.

One of the most important things to avoid is trying to squeeze, puncture, or cut a large lump yourself. Home drainage can cause bleeding, infection, scarring, or further tissue damage. A doctor or dermatologist can determine whether the safest approach is observation, drainage, medication, or surgical removal.

Medical evaluation is especially important if a lump is rapidly changing, becoming increasingly painful, draining fluid, or surrounded by spreading redness. Fever or other signs of illness also warrant prompt attention. Although many skin cysts are not dangerous, a persistent or unusual lump should be properly assessed rather than diagnosed from an image or treated at home.