Lumps behind the ear can have many possible causes, including problems in the skin or bone.

Swollen lymph nodes, infections, and certain cancers can also lead to lumps.

Most cases of a lump behind the ear do not present a cause for concern, however, and normally resolve without treatment.

There is a range of skin conditions and infections that can cause lumps behind the ear.

Lumps in the skin

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There are many possible causes of lumps behind the ear.

The three main noncancerous causes of lumps behind the ear are:

Acne lumps behind the ear

Acne is a common skin condition that might cause a lump behind the ear.

In acne, pores in the skin become blocked with sebum. Sebum is an oily substance secreted by units at the base of hair follicles.

The sebum mixes with dead skin cells and can form a layer called a comedone.

A pimple might then become infected and inflamed if certain bacteria enter the comedone.

Inflamed pimples can grow and, in their most severe form, form lumps called acne cysts.

If acne is causing the lump, it may cause pain when pressed. Other cysts and pimples on the head are likely to accompany pimples or cysts behind the ear, especially on the face.

Cystic acne is an unpleasant condition that can lead to scarring. Doctors can help manage cystic acne with effective treatments, however.

Cysts behind the ear

A cyst can occur anywhere in the skin, including behind the ear.

Skin cysts are fluid-filled sacs. They form a raised, dome-shaped area on the skin. Sometimes, they have a black spot called a punctum at the top.

They can move around freely and are not fixed in place. A doctor should examine any skin lump that cannot be moved from side to side.

Cysts in the scalp tend to be pilar skin cysts. In this type, the lining of the sac is made of hair root cells.

Sebaceous cysts can also occur. These form on the glands responsible for the oily substance that moisturizes the skin and hair.

Other cysts are made of cells from the surface of the skin, known as epidermoid cysts. Finally, there are also sebaceous cysts, which are less common and contain an oily substance.

Lipoma

Lipoma is another possible cause of lumps behind the ear. Lipomas are harmless, fatty lumps. They are not cancerous, grow very slowly, and do not spread.

They are more common on other parts of the body but can occur anywhere under the skin, including behind the ear.

A lipoma feels soft to the touch. They are not usually tender or painful unless they press on nearby nerves.

They will usually occur in a limited number of places. In rare cases, some people have many lipomas at once.

These lumps are often small and range from the size of a pea to inches across.

Cosmetic surgeons can remove unsightly lipomas, but it is safe not to receive treatment. If necessary, a surgeon can remove a lipoma.

Cysts and lipomas are similar types of lump. A lipoma sits deeper in the skin than a cyst, as well as feeling softer.

Enlarged lymph nodes

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Swollen lymph nodes can produce lumps behind the ear.

Lymph nodes grow behind the ear. These are parts of the immune system that drain and filter tissues.

The lymph nodes behind the ear are called the posterior auricular lymph nodes.

A lymph node can swell if exposed to foreign material. This might occur because of a nearby infection, for example. The formal name for this is lymphadenopathy.

A swollen lymph node should resolve without treatment. Skin or ear infections are common reasons for the node to swell.

If a lump lasts more than 2 weeks or occurs alongside other symptoms, visit a doctor.

Infections

The body reacts to infections by sending white blood cells to the affected area to combat the invading cells. This can lead to fluid buildup and swelling in the region.

Otitis, or ear infection, can cause this.

The part of the skull bone behind the ear is the mastoid. If bacteria infect this area of the skull, they might cause a condition called mastoiditis.

The infection takes place in the air spaces of the bone. The mastoid has a honeycomb-like structure. Bacteria can infect these air cells.

Mastoiditis is more common in children than adults. It is a serious infection that needs medical attention. The swelling behind the ear will be tender and red, and might cause the ear to be pushed outward.

Other symptoms may go with the lump, including:

The cause of mastoiditis is usually an untreated middle ear infection.

A doctor will treat mastoiditis with antibiotics to combat the infection. An ear, nose, and throat (ENT) doctor may treat some cases with surgery to drain or remove the infection.

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Visit a doctor if pain, redness, or tenderness accompany the lump.

Asking a doctor to examine a lump is safer than attempting to make a self-diagnosis.

It is especially important to visit a doctor about a lump if it meets the following criteria:

  • It is painful, red, tender, or has a discharge.
  • It is fixed in place or feels attached.
  • The lump changes or grows.
  • It appears suddenly.
  • It accompanies more general symptoms.

Lumps under the skin are less commonly result of cancer, but it is always safer to rule out potentially cancerous lumps with a doctor's visit.

If the lump is a tumor, a prompt diagnosis is important for the best chances of successful treatment. If a lump under the skin is cancerous, it is likely to be a soft tissue sarcoma.

Doctors will make a diagnosis by examining the appearance and texture of the lump.

They will ask a range of questions, such as the duration of symptoms and how they started. They will also refer to the medical history of a patient for a full picture of health.

Less commonly, a lump needs further investigation. This may involve taking a sample of tissue for analysis or carrying out an imaging test.