Other causes could be swollen lymph nodes, or "lymph glands" as they are commonly known.
Most cases of a lump behind the ear are not worrying and will resolve.
Lumps in the skin
A lump behind the ear in the surface of the scalp may be affecting the skin. Three noncancerous causes of skin lumps are:
Acne lump behind the ear
Acne is common in teenagers but can affect people of any age.
The common skin condition, acne, could explain a lump behind the ear.
In acne, pores in the skin become blocked with sebum. This is an oily substance secreted by units in the base of hairs.
Mixed with dead skin cells, the sebum forms a comedone. The pimple can then become infected and inflamed if certain bacteria get involved.
Inflamed pimples can get large. In the most severe form, they can create lumps known as acne cysts.
If the lump is caused by acne, it may be painful when pressed. It is likely to be accompanied by other cysts and pimples on the head, especially the face.
Cystic acne is an unpleasant condition that can lead to scars. Doctors can help to manage it with effective treatments, however.
Cyst behind the ear
A cyst can occur anywhere in the skin. A lump behind the ear could be a cyst.
Skin cysts are fluid-filled sacs. They form a raised, dome-shaped area in the skin. Sometimes they have a black spot on top known as a punctum.
They can be moved around freely and are not fixed down. Any lump that cannot be moved from side to side needs to be seen by a doctor.
Cysts in the scalp tend to be a form known as pilar skin cysts. The lining of the sac is made of hair root cells.
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 behind the ear
Lipoma is another possibility for a lump in the skin behind the ear. Lipomas are harmless, fatty lumps. They are not cancerous, grow very slowly, and do not spread.
Lipomas are more common on other parts of the body but can appear anywhere under the skin.
To the touch, a lipoma feels soft, a bit like bread dough. They are not usually tender or painful unless they are pressing on nearby nerves.
Lipomas are common but usually appear only in one or two places. In rare cases, some people have lots of lipomas.
The small lumps range from the size of a pea to a couple of inches across.
If the lump is not causing any cosmetic concern, it is safe to leave it untreated. If needed, a lipoma can be surgically removed.
Difference between cysts and lipomas
Cysts and lipomas are similar types of lump.
To tell the difference, a lipoma is deeper while a cyst is closer to the surface of the skin. Lipomas also feel softer than cysts.
Enlarged lymph nodes
Lymph nodes are found behind the ear. These are parts of the immune system that drain and filter tissues.
If lymph nodes are presented with foreign material, such as because of a nearby infection, they swell. The formal name for this is lymphadenopathy.
The lymph nodes are also known as lymph glands, in the same sense as "swollen glands" commonly known to affect the neck. The ones behind the ear are called the posterior auricular lymph nodes.
A swollen lymph node should go down on its own. Skin or ear infections are common reasons for the node to swell.
If the lump lasts more than 2 weeks or comes with wider symptoms, it is important to have it checked by a doctor.
The part of the skull bone behind the ear is known as the mastoid. If it gets infected with bacteria, this is a condition called mastoiditis.
The infection takes place in the air spaces of the bone. The mastoid has a honeycomb-like structure, with air cells that can get infected.
Mastoiditis happens more commonly in children than adults.
Mastoiditis is a serious infection that needs to be seen by a doctor for treatment. The swelling behind the ear will be tender and red and may cause the ear to be pushed outward.
Other symptoms may go with the lump, including:
- Ear discharge and possible loss of hearing
- High temperature
- Feeling unwell and irritable
The cause of mastoiditis is usually an infection in the middle ear that has not been treated.
Mastoiditis is treated with antibiotics to kill the infection. The condition is usually managed after a referral to specialist doctors that deal with the ears.
These ear, nose, and throat (ENT) doctors or otolaryngologists may treat some cases with surgery to drain or remove infection.
When to see a doctor
It is always best to ask a doctor to examine a lump. This is safer than attempting to make a self-diagnosis.
Always seek medical advice if any lump persists for 14 days or longer.
Even with good knowledge, self-diagnosis has a good chance of being wrong. Doctors are also in a position to help treat problems that are diagnosed.
It is especially important to have a lump checked if:
- It is painful, red, tender, or has a discharge
- Is fixed in place, or feels attached
- Changes or grows
- Appears suddenly
- Comes with other, more general symptoms
Lumps under the skin are less commonly because of cancer, but it is always worthwhile getting a lump checked to rule this out.
Tests and diagnosis
Doctors presented with a lump behind the ear will make a diagnosis mainly based on looking at the lump and feeling it.
They will ask questions such as how long the symptoms have lasted and how they came on. They will also refer to a patient's medical history.
Most lumps are diagnosed by examination and history-taking. Less commonly, a lump needs further investigation. This may involve a sample of its contents being taken for analysis, or an imaging test being done.