There are several different types of lumps that can appear at the hairline along the back of the neck. Common types of lumps include:

• Enlarged lymph nodes, also known as “swollen glands.” Lymph nodes usually swell because of infections, such as ear infections or infectious mononucleosis (“mono”). The lymph nodes on the back of the neck can also swell due to irritation of the scalp. Rarely, an enlarged lymph node on the back of the neck can signal a more serious problem, such as a tumor.
• Sebaceous cysts. These are normal oil glands in the skin, which become blocked and enlarged. They may be soft or firm. Occasionally, a sebaceous cyst can become infected, which may make it red, swollen and painful.
• Lipomas. These are benign (noncancerous) tumors produced by fat cells. Lipomas are usually soft and move easily, and tend to grow slowly. They rarely cause serious problems.

See your doctor if you have a swollen lump on the back of your neck that’s been present for more than two to three weeks, especially if the lump is painful or growing steadily. Your doctor will usually be able to tell what is causing the lump simply by examining you. The doctor may also ask you to come back in several weeks to get a better sense of whether the lump is getting bigger with time. Rarely, you may need to have the lump removed or biopsied to get a definite diagnosis.