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:

• face 
• neck or throat 
• breast 
• groin area  
• testicle   
• anus (bottom) 
• hand, wrist or finger 
• shoulders, back, chest or arm 
• armpit 

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

Click on the links above for more information about these conditions. 

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 – a harmless 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  

Click on the links above for more information about these conditions.

Lump in the breast

Breast lumps are common and have several different causes. While most breast lumps aren't breast cancer, any unusual changes to the breasts should be checked by a GP as soon as possible.

Common causes of breast lumps include:

• mastitis – painful, swollen breast tissue that is sometimes caused by an infection 
• enlarged milk ducts
• a non-cancerous growth (fibroadenoma)
• a cyst – a harmless fluid-filled lump
• a lipoma – a harmless fatty lump 
• a skin tag – a harmless, wart-like growth often found underneath the breast

Read more about breast lumps. 

Lump around the groin area

Common causes of a lump or lumps in the groin area include:

• a cyst – a harmless fluid-filled lump
• swollen glands – usually a sign of infection, such as a cold or glandular fever; the glands tend to go down when you recover
• a hernia – where an internal part of the body, such as part of the bowel, pushes through a weakness in the muscle or surrounding tissue wall
• an enlarged vein – known as a saphena varix, which is caused by a faulty valve inside the vein (the lump often disappears when you lie down)
• genital warts – small, fleshy growths caused by a sexually transmitted infection (STI)

Click on the links above for more information on these conditions. 

Lump or swelling in the testicle

Most testicular lumps are harmless and aren't cancerous. Less than 4 in 100 (4%) of testicular lumps turn out to be testicular cancer. 

A lump or swelling in the testicle is most likely to be one of the following:

• swollen and enlarged veins inside the scrotum (varicoceles)
• swellings caused by a build-up of fluid around the testicle (hydrocele)
• a cyst in the epididymis (the long, coiled tube behind the testicles)

Read more about testicular lumps and swellings.

Lump around the anus (bottom)

Anal swellings or lumps are usually one of the following:

• a haemorrhoid (pile) – a swollen blood vessel that can hang outside the anus 
• a skin tag – a harmless growth that hangs off the skin and looks similar to a wart
• an abscess – a painful collection of pus
• a rectal prolapse – where part of the rectum (the end of the bowel) sticks out of the anus
• genital warts – small, fleshy growths caused by a sexually transmitted infection (STI)

Lump on the hand, wrist or finger

A lump on the hand, wrist or finger is probably a ganglion cyst. This is a type of cyst that forms around the joints or tendons.

A ganglion cyst usually appears on the back of the wrist. It's made up of a thick jelly-like fluid and feels like a smooth, soft lump under the skin.

It's not clear why ganglions form, but they can be related to ageing or to injury to the joint or tendon.

If the ganglion doesn't cause any pain or discomfort, it can be left and may disappear without treatment. Otherwise, you may need to have it removed.

Sometimes, small rough lumps called warts develop on the hands. Warts are caused by an infection with the human papilloma virus (HPV) and are very contagious. However, they're usually harmless and clear up without treatment. 

Lump on the shoulder, back, chest or arm

A lump on the shoulder, back, chest or arm is most likely to be a lipoma or a cyst.

A lipoma is a soft, fatty lump that grows under the skin. It's fairly common, harmless and can usually be left alone. When you press a lipoma it should feel soft and "doughy" to touch. It can range from the size of a pea to a few centimetres across.

A cyst is a sac under the skin that contains fluid, usually pus. It can look a bit like a lipoma but is close to the surface of the skin (lipomas are deeper under the skin). Cysts are firm to the touch. A cyst may disappear without treatment or you may need to have it drained.

Lump in the armpit

A lump in the armpit is likely to be a swollen lymph gland, particularly if you also feel unwell and have other signs of an infection. The glands in the armpit can swell to more than a few centimetres in response to infection or illness. Swollen glands usually go down when you recover.

It's uncommon for a lump in the armpit to be a lymphoma (cancer of the lymph glands), but you should see your GP if the lump doesn't go down.

A small, knobbly lump in your armpit that hangs off the skin like a wart is probably a skin tag. Skin tags grow where skin rubs against skin or clothing, which is why they're often seen under the arm. They're very common and harmless, and can be left alone.