SAMPLE FAQ: Milk pimples (blebs, blisters)
What is a milk pimple?
Milk pimples look like white areas on the nipple face. They are typically 2 millimetres (1/8 inch) and can be flat or raised. Some pimples can be even smaller and others can be larger, affecting up to half of the nipple face. Most are circular but some can be star-shaped or irregular. New milk pimples can be very painful when a baby latches and hurt during the feed. They come on suddenly and there can be more than one present at the same time. Milk pimples are more common in women with a large milk supply and are associated with other problems such as plugged ducts and nipple vasospasm. There is virtually no research on what causes them or how to treat them. They may be caused by breast milk leaking from a duct under the skin or by the milk clotting. The body reacts to this with inflammation, which causes pain.
A) Describing milk pimples
Milk pimples are white spots or bumps that develop on the nipple face when breastfeeding. Mothers may only ever have one milk pimple but others may have numerous pimples which can appear at different times. They can recur in the same place or pop up elsewhere on the nipple.
They have other names:
- Milk (or nipple) blebs
- Milk (or nipple) blisters
“Milk pimples” seems to be the most widely accepted.
There are no studies showing what percent of breastfeeding mothers get milk blisters. In our Canadian clinic, we estimate that roughly 5% of the mothers we see have one or more milk blisters. An American clinic reported milk blisters in 17% of mothers seen (Mitchell 2020).
1) Initial appearance
Milk pimples are always found on the nipple face and are always white or creamy in colour. They can look like a flat patch or can be raised. They can be as small as 1 millimetre (1/16 inch) wide but occasionally they can be large enough to involve up to half of the nipple. Most pimples are about 2 millimetres (1/8 inches) wide.
Milk pimples usually have a circular shape but some can be star-shaped or irregular.
If a new pimple is opened, they may contain a cheese-like material. Rarely, the pimple contains stringy material.
2) Changes over time
Milk pimples will change in appearance as the body works to remove them. This can take up to eight weeks. The stages of healing are:
- A raised white pimple or irregular white patch appears on the nipple face.
- The pimple slowly turns more yellow.
- The edges become less sharp and blur with the skin surrounding the pimple.
- The pimple may peel one or more times.
- Tiny blood vessels and healthy tissue start to penetrate the area.
- The pimple starts to fade.
- The pimple disappears and no longer hurts.
Milk pimple can appear bloody or scabbed if they are opened. Repeated opening can cause the area around the blister to swell or scar.
Milk pimples do not usually appear during the first week after birth but can happen any time after that while breastfeeding. They are less common once the baby reaches one year of age.
Milk pimples will generally appear without warning. Some mothers have a plugged duct around the same time.
D) Type of pain
Milk pimples are usually tender to touch and cause a sharp pain with latching. The pimple can remain painful throughout the feed.
The amount of pain can range from mild to severe. They are most painful in the two weeks after they appear and then gradually settle.
E) Causes of milk pimples
There is virtually no research on what causes milk pimples, how to prevent them, or how best to treat them.
The author of one small study (O’Hara 2012) looked at the contents of a pimple under a microscope and found signs of inflammation but no signs of infection.
One thought is that pimples are caused by milk leaking from a milk duct and spreading under parts of the nipple skin. While most pimples are circular, we have also seen star- and irregularly-shaped pimples in which milk seemed to track under the skin, supporting this idea. This errant milk would cause the body to react with painful inflammation.
Another idea is that the milk has certain properties that makes it clot more easily, such as an abnormal breast microbiome (subacute mastitis) or the nature of the milk itself. Indeed, milk pimples and plugged ducts often develop around the same time, and it is possible they are both signs of the same problem.
F) Treatment and prevention
G) Other related conditions
Mothers who get milk pimples tend to get plugged ducts around the same time. Both are more common in mothers with a large milk supply.
Milk pimples can cause blanching of the nipples (nipple vasospasm) on one or both nipples.
Rarely, milk pimples that have been opened become infected.
It is possible that some of the larger, deeper milk pimples are actually cysts (fluid filled sacs) that develop when a gland that normally releases oil onto the skin becomes blocked.
Mitchell KB, Johnson HM. Breast Pathology That Contributes to Dysfunction of Human Lactation: a Spotlight on Nipple Blebs [published online ahead of print, 2020 Jun 3]. J Mammary Gland Biol Neoplasia. 2020;10.1007/s10911-020-09450-7
O'Hara MA. Bleb histology reveals inflammatory infiltrate that regresses with topical steroids; a case series [platform abstract]. Breastfeed Med 2012;7(Suppl 1):S-2
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