Most lumps and swellings under the skin are harmless and can be left alone, but should be checked by a GP so the cause is known.

In general, a painful lump or swelling that appears suddenly over a day or two is usually 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 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 a better idea of what your lump or swelling may be. However, do not 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 was not 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 – this is known as 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 can 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 on these conditions. 

Lump in the neck or throat

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

• swollen glands – usually a sign of infection, such as a cold or glandular fever, and 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, which causes a lump to form in the throat  

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

Lump in the breast

Breast lumps are common and have several different causes. While most are not 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 which may be caused by an infection 
• enlarged milk ducts
• a non-cancerous growth – called a fibroadenoma 
• a cyst – a harmless fluid-filled lump
• a lipoma – a harmless fatty lump 
• a skin tag – a harmless, wart-like growth often found hanging underneath the breast

Find out more information on these and other possible causes of 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, and tend to go down when you recover
• a hernia – an internal part of the body, such as a part of the bowel, which 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 and swellings are harmless and not cancerous. Cancer Research UK estimates that less than 4% of testicular lumps are testicular cancer. 

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

• an enlarged vein inside the testicle – called a varicocele
• a build-up of fluid around the testicle – known as a hydrocele
• a cyst in the epididymis (the long, coiled tube behind the testicles)

Find out more information on these conditions and other possible causes of 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 a bit like 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. 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 feels like a smooth, soft lump under the skin. It is made up of a thick jelly-like fluid.

It’s not certain 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 the ganglion removed.

It is also common to develop small, rough lumps called warts on the hands. These are caused by an infection with the human papilloma virus (HPV) and are very contagious. They are generally harmless and usually 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 is fairly common, harmless and can usually be left alone. When you press a lipoma, it should feel smooth and soft, like rubber or dough. 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 skin surface (lipomas are deeper under the skin). Also, cysts are firm to the touch. A cyst may go away on its own without treatment, or you may need to have it drained.

Lump in the armpit

An armpit lump is likely to be a swollen lymph gland, especially 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 disease. Swollen glands tend to go down when you recover from the illness.

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

If the lump in your armpit is small, knobbly and hangs off the skin like a wart, it is likely to be a skin tag. It is thought that skin tags grow where skin rubs against skin or clothing, which is why they are often seen under the arm. Skin tags are very common and harmless, and can be left alone.