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One of the most common questions I get from breastfeeding moms is what to do when one breast produces more milk than the other. Moms want to know if this is normal and if they should be concerned about it. 

When One Breast Produces More Milk

Having an uneven breast milk supply is actually more common than both breasts producing the same amount of milk (Source).

Some women affectionately call their lower producing side their slacker boob or milk dud. 

I’ll go over the possible reasons for this common phenomenon and what, if anything, you should do about it.



There are two common reasons that one breast produces more milk than the other.

One explanation has to do with mom. The other reason is because of the baby. It’s also often probably a combination of the two.

Let’s dive a little deeper into both possible causes for why one breast makes more milk.



Uneven Milk Supply Due To Mom

  • One breast might have more of the breast tissue that is responsible for making milk. Humans are not perfectly symmetrical. One foot is usually larger; one arm may be a bit longer. Most women start out with one breast that is slightly larger than the other. Some might have a significant difference in the size of their breasts. In addition to making bra sizing a challenge, it can affect how much milk each breast can make.
  • Milk might flow faster on one side. 
    • This might be a natural occurrence due to having more nipple pores on one side.
    • A mom might have a difference in how forceful her let-down is on each side.
    • A history of having any kind of breast surgery potentially can impact milk flow. Some breast surgeries can cut milk ducts. Scar tissue can also affect flow.
    • Even a breast biopsy has the potential to alter milk flow.
    • An injury to the breast or having chest tubes at any point in a person’s life can affect flow.
  • Radiation therapy for breast cancer can affect milk production (Source).
  • Some women have nipples that are shaped differently from each other, or one is larger than the other, and a baby may find one is easier to latch onto, or they prefer the feel of it in their mouth. This is very common when one nipple is flat or inverted, and the other nipple is protuberant.
  • Most women have one side that they feel more comfortable nursing on. They may unwittingly be offering that side first more often. 

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woman covering her breast and blue gloved hand drawing lines under her breast

Uneven Milk supply Due To Baby

  • Many babies show a preference for one breast over the other.
    • This may be because the milk flows at a rate more to their preference. 
    • If one side flows faster, they may prefer that. They also may like a slower flow. 
    • Your baby may feel more comfortable the way they are positioned on the preferred side.

Spending more time on one breast means more stimulation on the higher producing side. This is one of those things that becomes a cycle. The baby prefers one breast and spends more time on it. That breast gets more stimulation and may produce even more milk. The lower producing side gets less stimulation, and supply decreases. Baby gives the slacker boob even less time and stimulation.

It is hard to tell whether a baby causes a difference in milk production because they have a preferred breast or they end up preferring one breast because of the uneven milk supply.

When One Breast Produces More Milk


There are two primary reasons why a mama worries about one breast taking on the lion’s share of milk production.

Usually, a mom’s primary concern is whether their baby is able to get enough milk to grow normally.

If your baby is getting what she needs, you don’t need to stress, even if one breast barely produces milk. 

If your baby is growing at an average rate, then she is getting the amount of milk that she needs. 

The other reason a mother frets over uneven supply is it can result in lopsided breasts. Some women won’t care, even if the difference is significant. Other moms might find the difference cosmetically unappealing.

One breast producing more that results in a much larger breast also could cause physical discomforts for a woman. Common complaints are neck, back, or shoulder pain.

When One Breast Produces More Milk

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  • When pumping, you consistently get more milk from one breast.
  • Your baby nurses longer on one side compared to the other.
  • Your baby shows a preference for one side.
  • One breast feels fuller.
  • The higher producing side is noticeably larger.


Mastitis can cause a decrease in milk supply. This is usually temporary. With regular stimulation and draining the breast as much as you can, the supply should come back to normal within a week.

A clogged duct is another temporary cause of an unequal supply.

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If having an uneven milk supply makes your breasts’ size noticeably different or you have an insufficient milk supply, you may want to try to even things out.

  • First, make sure you are alternating which side you offer first. You can keep track of which side with an app. If you don’t want to be tied to your phone all the time, you can wear a nursing bracelet like the easy to use Which Side. On one side, it says Left and Right on the other side. You simply flip it over each time you nurse. 
  • If you are alternating sides each time, then try offering the lower producing side first. If your baby gets frustrated, then do breast compression to keep him happy with the flow. This can help drain the breast more thoroughly. When a breast is well drained, it tells the breast to make more milk.
  • Provide some extra stimulation by pumping on the side that produces less milk right after feedings. If you are comfortable with it, you can pump on that breast while you breastfeed on the other side. 
    • Do hands-on pumping.
    • Use the LaVie Lactation Massager to help empty your breast. Moms love how this gadget helps them get more milk out. It can be used during pumping or breastfeeding.
  • You can use an electric breast pump or a wearable pump like the Willow. Another option is putting on a Haaka pump.
  • Do a daily power pumping session on the breast you want to produce more milk.
  • Try different nursing positions on the breast your baby doesn’t like as much. If you do the cradle hold, try football hold, or vice versa.
  • Put a warm pack on your breast to increase the flow. The Milkease All Natural Breastfeeding Relief Pack was designed for this. Research has shown that warmth on the breasts during pumping helped moms pump more milk (Source). It makes sense that it can help with breastfeeding also.

When One Breast Produces More Milk

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Many women can make a full milk supply on one breast. Think of the moms who make enough milk for twins.

I worked with a mom once who’d had radiation to one breast, and that breast didn’t make any milk when she had her baby. She was able to make all the milk her baby needed on her one working breast.

A mama’s breast can’t make unlimited amounts of milk, though. It is possible if one side is very low producing the other breast may not be able to pick up the slack. At the end of the day, you provide as much breast milk as you can. 



Although having a difference in supply between breasts can be concerning, there is no need to worry if your baby is growing and you are not having any discomfort. 

There are also many different ways to encourage a slacker boob to do more of their share of the work. 

For most moms having a difference in how much milk each breast produces is common and can go on the list of interesting things to know.