Most lumps and swellings under the skin are harmless and can be left alone. However, see your GP if you develop a new lump or swelling so that the cause can be identified.

A painful lump or swelling that appears suddenly over a day or two may be caused by an injury or infection. It's likely to be an infection if the skin around the lump is red and warm. Your GP can advise you about how to care for this.

Below are some of the most common reasons for an unexplained lump or swelling under the skin in the following areas of the body:

This information should give you an idea about what your lump or swelling might be. However, don't use it to diagnose yourself with a condition. Always leave that to your doctor.

Facial swelling or lump

A lump or swelling on the face that wasn't caused by an injury is most likely to be one of the following:

• mumps – a viral infection that usually affects children and causes swelling of the glands on the side of the face

• an allergic reaction – for example to peanuts, which causes swelling in the deeper layers of the skin (angioedema)

• a dental abscess – that causes the side of the mouth to swell

• a salivary gland stone – this forms when the chemicals in saliva crystallise and block the flow of saliva from a salivary gland near the jaw, causing pain and swelling around the jaw

Lump in the neck or throat

A lump in the neck or throat is most likely to be one of the following:

• swollen glands – usually a sign of infection, such as a cold or glandular fever; the glands tend to go down when you recover

• a cyst – aharmless fluid-filled lump that may disappear on its own without treatment (it will feel like a pea and roll under the skin when you press it)

• a skin tag – a harmless, knobbly wart-like growth that hangs off the skin and can be left alone

• a goitre – an abnormal swelling of the thyroid gland in the neck that causes a lump to form in the throat

When to see your GP

See your GP if you develop a growth or swelling on your body. They can examine it and confirm what it is and what's causing it.

If your GP is uncertain, they may recommend that you have an ultrasound scan or a biopsy. Surgery may be needed to remove certain types of lump.

You should also see your GP if you have a lump that:

• is getting bigger

• is painful

• feels hard

• grows back after it's been removed