Open a PDF version to print this topic

HealthInfo Canterbury

Causes of breast lumps

Several different things can cause lumps in your breast. Most of them aren't cancer and aren't dangerous. But if you find a lump in your breast, it's important to get your GP to check it.


The most common cause of a non-cancerous (benign) breast lump is a fibroadenoma (fie-bro-ad-en-o-ma). These lumps are caused by an overgrowth of glands and connective tissue in your breast. They're most common in younger women, most commonly in their 20s, but can happen right up to menopause. Hormone levels affect them, so they can grow larger during pregnancy and smaller after menopause.

These lumps are round and smooth, and sometimes feel rubbery. They aren't usually tender and can also move around a lot. This is why a fibroadenoma is sometimes called a “breast mouse”.

Often fibroadenomas eventually disappear, especially after menopause. Occasionally women have surgery to remove a large one, or one that's causing discomfort. Fibroadenomas don't turn into cancer, so it's quite safe to leave them alone.

Breast cysts

Cysts are another kind of lump that can form in your breasts. They're fluid-filled sacs and can feel like smooth round lumps. If you press them, they can move slightly, but they don't move as much as fibroadenomas.

Simple cysts are normally benign (non-cancerous). Women can get them from their early 30s until after menopause. Most cysts go away without treatment, but larger cysts can be painful and may need to be drained.

Very rarely, some complex cysts need a biopsy as some of them can be cancerous.


Breast infection usually happens in women who are breastfeeding.

Infection can happen because your milk ducts get blocked and the milk can't flow from that part of your breast. Also, bacteria (germs) can enter through your nipple, causing an infection.

Infection can cause mastitis, which makes your breast hot and tender, with a firm swelling. Sometimes this can develop an abscess (a cavity containing pus), which feels like a lump in your breast. If an infection gets to this stage, you may need surgery to open the abscess and drain the pus. You'll also get some antibiotics to take, and advice on how to stop it happening again.

Fat necrosis

If you've injured your breast, the injured fatty tissue can cause a lump. This is harmless, but it may be present for quite some time before it goes away. Occasionally fat necrosis doesn't go away, but if it's causing a problem you can have surgery to remove it. Fat necrosis is harmless and won't turn into breast cancer.


Sometimes a fatty growth called a lipoma can develop in your breast (and other parts of your body). This is a benign (non-cancerous) growth that usually doesn't cause any symptoms and can be safely left without any treatment. But if you have a large lipoma that's causing problems, you can have surgery to remove it.

Intraductal papilloma

An intraductal papilloma (in-tra-duck-tal pap-il-lo-ma) is a wart-like growth in your ducts, often close to your nipple. It's also sometimes called ductal papilloma or papilloma of the breast.

It can feel like a small lump, but sometimes it just causes a blood-stained fluid discharge from your nipple. Sometimes a breast-screening mammogram picks up an intraductal papilloma. These growths can sometimes have abnormal cells and there's a small risk of them becoming cancerous, so they're usually removed by a breast surgeon.

Breast cancer

Most breast lumps are not caused by breast cancer. But because breast cancer can cause a lump in your breasts, it's important to get your GP to check any new lump you find.

  HealthInfo recommends the following pages

On the next page: What to do if you find a lump in your breast

Written by HealthInfo clinical advisers. Endorsed by oncoplastic breast and general surgeon, Canterbury DHB. Page created December 2018.


Page reference: 406143

Review key: HIBRL-129242