Noticing a bump, lump, or unusual growth on the back of your head can naturally cause concern, but there are several possible explanations, and many are harmless. A common cause is a **pilar cyst**, which can develop around a hair follicle and appear as a smooth, firm lump beneath the skin. Other possibilities include an **inflamed hair follicle, ingrown hair, lipoma**, or a swollen lymph node. In some cases, irritation from hairstyles, hats, sweating, or minor skin injuries can also contribute to a noticeable area on the scalp.