Lump in armpit? Find the cause and how to treat it

Finding an armpit lump can be worrying but in many cases it's nothing serious. See our checklist to find possible causes and when to see a doctor or self-treat.


Lump in armpit – why does it develop? 

What are the causes?

What your armpit lump could be:

When should I worry?

It’s normal to feel anxious if you find a lump under your armpit, but is it something to worry about? 

In most cases, an armpit lump will be harmless, but it’s important to know what may have caused it and if it’s something you should see a doctor about. 

If your lump has been there for more than two weeks or it’s getting bigger, you should see a doctor as soon as possible.

## Lump in armpit – why does it develop? 

Your armpit is located under your shoulder joint, where the arm connects to the shoulder. It contains nerves, blood vessels and small glands known as the lymph nodes. 

An armpit lump is any growth on your skin in this area that normally shouldn’t be there. 
Lumps can appear anywhere on your body. If you find a lump, you shouldn’t ignore it.

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## What are the causes?

### 1. Swollen lymph nodes

Your lymph nodes play a role in your immune system and if your body is fighting an infection, these glands may swell. 

This is part of your body’s natural defences and is a symptom of being unwell, so rest and stay hydrated to help you recover, by which time your glands should have gone down.

### 2. Cyst

Cysts are fluid-filled lumps that form under the surface of your skin. Certain types of cyst (Pilar cysts) form around hair follicles, such as those under the arm. But they are found on your scalp more often.

These types of cysts typically affect middle-aged women and can run in families. An armpit cyst is harmless and may clear up without treatment.  

### 3. Lipoma

[Lipoma](/skin-changes/lipoma) are soft lumps of fat that grow under your skin. They don’t often appear in the armpit, but are nothing to worry about when they do, and don’t generally require treatment. But keep a check to monitor how long they've been there (see When to see a doctor, below).

### 4. Breast infection

A breast infection (or [mastitis](/after-pregnancy/mastitis)) causes a woman’s breast tissue to become inflamed, and sometimes a lump may appear under the arm due to the spread of the infection to the lymph nodes. 

It’s more common in breastfeeding women, and usually affects only one breast. You may need antibiotics to treat it, so a visit to the doctor is necessary.

## What your armpit lump could be:

Whether you have a painful lump in armpit or it doesn't hurt but is swollen or is hard to the touch, check this list to see what might be the cause.  

1. *Is the lump yellow or white in colour and filled with pus?*

If yes, then it may be a cyst. These are usually painless but can be tender and sore if they become infected.

2. *Does the lump feel soft and move slightly under the skin when you press it?*

If yes, you may have a lipoma. They aren’t usually painful and tend to grow slowly, and they can range from the size of a pea to a few centimetres across. 

3. *Does the lump feel tender and painful? *

If it does, then you may have swollen lymph nodes. These tend to go down on their own after 2 or 3 weeks once you’ve recovered from the infection.

4. *Is the lump wedge-shaped or hard to the touch?*

If so, your armpit lump may be caused by a breast infection that’s spread to your lymph nodes. Your breast may be red and swollen too.

Occasionally, an lumps in armpit may be a sign of something more serious, such as [breast cancer](/breast-cancer/breast-cancer-in-women) or [Hodgkin’s lymphoma](/blood-cancer/hodgkins-lymphoma). If you’re not sure or are worried, always see a doctor.

## When should I worry?

Ask yourself the following questions:

1. Has the lump been there for more than 2 weeks?
2. Is the lump getting bigger?
3. Have I lost weight without trying to?
4. Do I have any other symptoms I can’t explain?
5. Has the lump returned after being removed?

If you answered yes to any of these questions, it’s best to see a doctor as soon as possible.

They should be able to identify what’s caused the lump to appear. If they’re unsure, they may refer you to hospital for further tests, such as a [biopsy](/surgical-procedures/biopsy) or [ultrasound](/medical-imaging/ultrasound-scan) scan.

If you’re looking for more information on the different types of lumps and what causes them, read our article on [lumps and swellings](/skin-changes/lumps-swellings).

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Finding an armpit lump can be worrying but in many cases it's nothing serious. See our checklist to find possible causes and when to see a doctor or self-treat.