Finding a lump on the neck, back, or behind the ear can be worrying, especially when it appears suddenly or feels unusual. While many lumps are harmless, some may point to a health issue that needs attention. Lumps can vary in size, texture, and how long they last, which makes it important to notice any changes.

Some lumps disappear on their own, while others persist, return, or slowly grow over time. Understanding possible causes can reduce anxiety and help you know when medical advice may be necessary.

One of the most common explanations is an epidermoid cyst. It is a “benign, noncancerous growth that forms just beneath the skin.” These cysts usually grow slowly and are most often found on the neck, back, face, or behind the ears.

Epidermoid cysts develop when skin cells that normally shed become trapped under the surface. The cells continue multiplying, forming a sac filled with keratin, a “thick protein found in hair and nails.” In most cases, these cysts are painless and harmless.

However, they can sometimes become irritated or infected, leading to “redness, swelling, tenderness, or discomfort.” Although anyone can develop an epidermoid cyst, they occur more often in adults than children and are more common in men. Knowing how these lumps form and when to seek medical care can ease fear and help ensure potential problems are addressed early.