Breast Lumps

Although it is always worrying to find a breast lump, lumps that come and go or change size as your breasts fill and empty with milk can be quite common when you are breastfeeding.1 If there is a significant build up of breast milk in the breast this could cause engorgement, blocked ducts and mastitis which are each associated with swollen, lumpy breasts sometimes referred to as breast inflammation. If breast inflammation is not treated promptly this could lead to another type of breastfeeding related lump; a breast abscess. Lumps in the armpit may also occur in lactation because breast tissue extends into the armpit. Other possible causes of lumps include milk-filled cysts (galactoceles), benign cysts, and tumours (fibroadenomas).

This article looks the most common causes of breast lumps during breastfeeding and shares where to get more information.

Check with a health professional

It is important to check with your health professional about any lump that doesn’t disappear after a week or so, or that you have any concerns about. Persistent breast lumps may need medical investigation to determine their cause. For most conventional tests such as ultrasound, mammogram, CT scan, MRI scan, needle biopsy and core biopsy; breastfeeding need not be interrupted. The article Medical Tests While Breastfeeding provides more information, further reading and references about the compatibility of various tests while breastfeeding.

Breast lumps that come and go in the breasts or even the armpits are not unusual when breastfeeding

Common causes of breast lumps while breastfeeding

A common cause of lumpy areas in the breast during breastfeeding is breast inflammation due to a build up of excess milk. Breast inflammation may be caused by infrequent breastfeeds, poor positioning (the way baby is held to feed), latch (the way a baby is attached to the breast), or something pressing into the breast to obstruct the flow of milk. Engorgement, blocked milk ducts, mastitis, galactoceles and breast abscesses are all forms of breast inflammation. An IBCLC lactation consultant or breastfeeding helper can be very helpful to find the cause of breast inflammation by watching your baby breastfeed and discussing breastfeeding management.


Engorged breasts (full tender breasts which may feel lumpy) when your milk first comes in and in the first few weeks after your baby’s birth can be quite normal, but swollen lumpy breasts at other times may mean your baby isn’t draining the milk from all areas of the breast equally.2 This could be due to suboptimal positioning and attachment, infrequent feeds or something else. See Engorged Breasts for further help.

Blocked milk duct

If engorgement worsens in one area of the breast it can affect milk flowing freely in that area and potentially affect other areas of the breast. The build up of milk is thought to cause the fine milk ducts that carry milk to the nipple to flatten or close—creating a lump and tenderness as the area gets engorged. The pressure of excess milk causes breast inflammation that is often referred to as a blocked milk duct or, as it worsens; mastitis (see next section). A phlegmon is another name sometimes used for an area of inflammation in the ducts associated with recent or ongoing mastitis.3  See Blocked Milk Duct for much more information.


When engorgement or blocked ducts are not relieved promptly a mother may get symptoms of mastitis which causes severe breast pain in addition to symptoms that can extend to the whole body. The mother may feel generally unwell with flu type symptoms such as feeling achey and shivery. If it isn’t managed carefully, mastitis may be associated with an infection requiring antibiotic treatment. See Mastitis Symptoms and Treatment for much more information to prevent and treat mastitis.

Breast abscess

Between 3–11% of women with acute mastitis may develop a breast abscess.4 The abscess is a pocket of pus contained within the breast and is more likely to develop following painful engorgement or mastitis that wasn’t treated promptly. An abscess will usually be felt as a painful, swollen lump inside the breast, and a mother may have a high temperature. For more information about diagnosis and urgent treatment see Do I Have a Breast Abscess?


A galactocele is a harmless, milk filled cyst (a fluid-filled lump under the skin). It is thought to form when ducts are narrowed by engorgement causing a significant volume of trapped milk to collect in a cyst (Mitchell et al, 2022). The contents of the cyst may be milk or semi solid material (Douglas, Vol 18: 1–20 2022). A galactocele can vary in size from small (1–2 cm) to very large (>10 cm) and may fluctuate during the day being smaller after a breastfeed (Mitchell et al, 2022). The galactocele feels like a smooth, round, moveable sac inside the breast. It is not usually painful or tender. Squeezing the galactocele may cause milk to be expressed from the nipple.5 A diagnosis can be made by a breast ultrasound6 or by taking a little sample of the contents of the cyst by fine needle aspiration. Occasionally a galactocele may become infected and need draining but usually the cyst will disappear when breastfeeding ends (Mitchell et al, 2019).

For symptomatic galactoceles, drainage is recommended for symptom relief, confirmation of diagnosis, and to decrease mass effect to facilitate latch. Aspiration almost always results in incomplete drainage and/or recurrence, and repeated aspirations risk converting a sterile galactocele into an infected galactocele.


For further information about diagnostic tests and the radiological appearance of a galactocele see Galactoceles (, Steven Halls, accessed 21 July 2022).

Lumps in the armpit?

Breast tissue extends into the armpit and it has a special name the “Tail of Spence”. During engorgement, for example when your milk first comes in, you may notice lumps and swelling in your armpits. Using the tips in Engorged Breasts can help to reduce this engorgement. It is also possible to have extra breast tissue that is not connected to the breast both in the armpit and in other areas of the body. Again this “accessory” breast tissue may become engorged when your milk first comes in but should resolve after a week or two. For more information about these types of swelling when breastfeeding, see Kelly Bonyata’s article below.

Lactating adenoma

A lactating adenoma is a painless benign tumour appearing in the breast during late pregnancy or during breastfeeding.7 They can grow rapidly due to hormonal stimulation and disappear spontaneously when breastfeeding ends (Mitchell et al, 2019).

Breast lumps unrelated to breastfeeding

Breast cysts and fibroadenomas

Examples of benign (non cancerous) breast lumps include breast cysts (fluid filled lumps) and fibroadenomas (solid lumps). Cysts and fibroadenomas within the glandular or milk making tissue could have the potential to impede milk flow or cause a blockage in an area of the breast. If an area of the breast cannot drain it will begin to shut down milk production in that area of the breast. Occasionally depending on the symptoms, size and position of the cyst or fibroadenoma a mother may decide to stop breastfeeding on one breast while continuing on the other side.

The problem with adenomas is that they can cause blockages and impairments to normal breast function.  In addition, adenomas can also be a sign of hormonal imbalances.

Lawrence and Lawrence say that cysts should be removed and biopsied but won’t interfere with breastfeeding. They add that pregnancy and breastfeeding can stimulate the growth of fibroadenomas that are related to the menstrual cycle. NICE guidelines discuss diagnosis techniques and treatment options for symptomatic breast fibroadenomas including high-intensity focused ultrasound8, and see Fibroadenoma of the Breast (Steven Halls, 2019) for more reading.

Fibrocystic breasts

Fibrocystic breast condition (previously called fibrocystic breast disease) is a benign breast condition that encompasses a group of symptoms in the glandular breast tissue such as breast pain, solid lumps and cysts (fluid filled sacs). Some authors advise reducing caffeine in the mother’s diet to improve symptoms 9 or taking vitamin E supplements 10. Lawrence and Lawrence report that fibrocystic breasts can be associated with a bloody discharge from the nipple during pregnancy and lactation but generally the syndrome is not a contraindication to breastfeeding.

Rare causes of breast lumps while breastfeeding

Breast cancer

It is very rare for a lump to be a sign of cancer especially while you are breastfeeding but always get medical advice if the lump is still there after a week 11, and particularly if it is getting bigger, does not move, is firm and hard, or if there is dimpling of the skin.

Most women worry that they may have cancer when they discover a breast lump. Studies have shown that breastfeeding reduces a mother’s risk of breast cancer. However, a lump that does not go away after a week or recurs in the same place despite careful treatment for a blocked duct, needs checking. In many cases breast lumps are benign tumours (fibromas) or milk-filled cysts (galactoceles) which can be diagnosed and treated whilst you continue to breastfeed. It is very rare for a lump to be a sign of cancer. But do consult your doctor, especially if the lump continues to grow, does not move, or is firm and hard, and if there is dimpling of the skin.

Inflammatory carcinoma of the breast

Inflammatory breast cancer is a rare type of breast cancer where the whole breast can look red and inflamed and be very sore. This could occasionally be mistaken for mastitis. Jack Newman, Canadian paediatrician and breastfeeding expert explains:

This type of cancer can occur at any age but it is uncommon. It is a particularly aggressive type of breast cancer and sometimes the mastitis-like symptoms can come on over a day or two. The breast may swell rapidly and be quite red. A hint that this is different from typical mastitis is that the skin may have a peau d’orange (orange peel) appearance. Sometimes the nipple is retracted as well.


Breast lumps that come and go in the breasts or even the armpits are not unusual when breastfeeding. Possible causes of breastfeeding related lumps include engorgement, blocked ducts, mastitis, and galactoceles. It is rare for a lump to be a breast abscess or a sign of cancer but it is important to get medical advice if the lump is still there or increasing in size after about a week to rule this out. Most diagnostic tests are compatible with breastfeeding.

This article should not be construed as medical advice. Always confirm the nature of persistent breast lumps with your medical professional.