Lipase and Sour Breast Milk

Lipase is an enzyme that is naturally present in human milk. It has several very beneficial dietary functions such as:

– Aids in keeping the milk fat emulsified (or mixed well) with the  protein portion of the milk known as the “whey”.

-Keeps the fat globules tiny so that the body can easily digest them

-Helps to break down the milk fat enabling the fat soluble nutrients such as certain vitamins (A&D) and free fatty acids (responsible for protecting the baby’s immunity) become more easily absorbed by the body.

Some mothers may notice their expressed milk will have a “soapy” appearance and taste that becomes rancid rather quickly after being stored. This is a rare condition resulting from an excess of the enzyme lipase in their milk. Lipase is responsible for breaking down the fat in the milk. If there is an excess of this enzyme then the fat gets broken down to quickly after being expressed thus resulting in the change. The milk is not harmful, and most babies are not bothered by the mild change. However, the longer the milk sits the more apparent the taste/smell becomes which then will result in the baby most likely having an aversion to it.

Once the milk has soured or become “soapy” there unfortunately is nothing you can do to reverse the state the milk is in. However, there is something you can do to help prevent the bothersome change with future expressed milk. If you are certain that your milk storing issues are related to an excess of lipase, you can try scalding the milk prior to storing it in the freezer or fridge. Scalding the milk soon after it is expressed with stop the breakdown process of the fat properties resulting from the access enzymes. To scald, heat the milk in a pan on the stove to around 180 degrees F, or until you begin to see bubbles forming around the edge of the pan. DO NOT bring the milk to a rolling boil. Once the proper temperature has been reached, immediately cool the milk down and store in an air tight container.

It is true that scalding the milk at such a high temperature will result in killing some of the antibodies and pro-biotic features of breast milk, however there are still many valuable components to breast milk that will still provide better nutrients to your baby then store bought formula. As long as your baby is receiving breast milk directly from the source a couple times a day, and yes momma that means you, loosing the additional antibodies from the heat treated milk shouldn’t be a problem.

For further information consult with a Licensed Dietitian or Lactation Consultant.


Lawrence R, Lawrence R. Breastfeeding: A Guide for the Medical Profession, 6th ed. Philadelphia, Pennsylvania: Mosby, 2005: 156-158, 203-205, 771, 781.


Copyright© 2011 Danielle Gauss/ All Rights Reserved

This entry was posted in Breast Milk Storage Guidelines, Diet Concerns. Bookmark the permalink.

35 Responses to Lipase and Sour Breast Milk

  1. Angela says:

    Can an excess of lipase in breast milk be associated to taking Licethin supplements to reduce clogged milk duct issues?

    • Admin says:

      I have not heard of that ever being an issue, but I will research the topic and get back to you. Usually lipase is associated with something completely different. Lecithin is a poly-unsaturated fat designed to make milk less sticky, it shouldn’t have anything to do with the lipase. However, I’m always interested in doing research, I will look into it for you.

  2. mercedes says:

    my ob told me i have “sour milk” but its not after i store it. its straight from the source. what does that mean? and how can i fix it? he was not very helpful at all.
    and when the problem is fixed will i be able to breastfeed again?

    • Admin says:

      This is very interesting to me as usually the lipase reaction happens once air hits the milk causing it to sour. Usually the milk coming straight from your breast to baby’s mouth wouldn’t be sour and I’m not sure how the OB would know that. Is it smelling sour after you have pumped prior to storing? Or is the OB saying that somehow the milk is sour prior to expressing?

      • Amanda says:

        Hi, my Breastmilk is also sour directly from me, my baby started projectile vomiting two days ago after every feed. I just decided to express milk now and taste it myself as something is obviously wrong and it was sour, why would this be and what would be the cause of it…? Any advise and/comments…?

        • Admin says:

          Are you taking any new medications such as birth control or are you working out more then before? Lactic acid from exercise can cause milk to be bitter. Just a sign that you may need to increase your water.

    • Kitty Rader says:

      Hello, I am an IBCLC. One of my patients asked me about her milk ‘souring’. I had not heard of that before and found your website. This patient is a diabetic and on an insulin pump. Could this have anything to do with the ‘sour’ milk smell? I told her the milk is fine and she can feed it to her baby. Any suggestions would be helpful. I will give her the scalding information.


      • Admin says:

        Hi there. It is possible that there is a link with insulin and lipase, as the lipase reaction does have to do with sugars in the body. However, I don’t know if there is a study to back that theory up. I will definitely research it and let you know what I find. In the mean time, yes the milk is fine, and scalding will help. You can also have her try pumping directly into sterile bags vs. a bottle as this does seem to help decrease the problem. Best of luck, and I am so glad you found my site helpful.

  3. Ryan says:

    I have not been quickly cooling after bringing to 180 degrees but letting it sit out until it cools then freezing. I also left out 4 oz the other day for 3 hours accidentally after scalding. Is it still safe to use or should I toss all of it. I am now submerging in ice water after scalding. Also do you know why it has to be “quickly cooled”

    Thank you!

    • Admin says:

      The quick cooling helps keep the milk at it’s correct molecular level so that there are no more lipase effects. The milk you left out should be just fine, unless it still has the sour smell to it.

  4. JOy says:

    I’ve had a few run ins with this now – just finding out today it may be Lipase.
    I pump 2x a day during the week and the baby gets this the next day – he nurses directly from me otherwise morning and evenings. We have only ha dthis issue of soapy, yellowy, sour milk a few times. It is not my storing of the milk at all. So since it seems to not be an everyday thing – could it be related to something I am eating? – Too much sugar, too much fat, etc?

    • Admin says:

      It could be related to something in your diet, as that most definitely plays a role. I would keep a food diary and see if you can pinpoint specifically what it is you eat on the days that you have a lipase reaction. Usually it is due to high amounts of fat.

  5. Sue says:

    I have issues with my breastmilk going sour after I freeze it then heat it up to feed to baby. It’s fine when I freeze it and thaw it out but as soon as I heat it up to feed it to baby it instantly goes sour? I’ve even tried letting it sit out and warm up at room temp and it still goes sour.

    • Admin says:

      It sounds like a lipase reaction. Your best bet would be to scald the milk prior to freezing as mentioned in my article to help minimize the lipase reaction, or trying to lower your fat and sugar intake to see if that helps. Best of luck to you.

  6. Amina says:

    After expresseing my milk, i store in the refrigirator immediately. When i use the milk after 24 hours or so it looks like it has soured. No bad smell or taste but looks like slightly curled milk. Looks like the fat has separated form the milk. I shake the milk evenly everything looks fine but after 5 mins again it looks like slightly curdled. Is the lipase reaction? If the milk is stored in refrigerator used within few hours or so everything is fine. Please advice.

    • Admin says:

      Breast milk will separate and look as if it has curdled. All that is happening is the fat and protein are rising to the top and the water is sinking to the bottom. This is normal, and just means your milk is healthy. Just shake it and warm it in a basin of warm water, and you should be just fine.

      • Amina says:

        Thanks for your quick reply Admin. I will try what you have suggested.
        Do you think i should scald the milk? Any website to teach me how to scald the milk in the right way?

  7. cherylwcs says:

    Hi..can i refridgerate the newly expressed milk then only scald it? After scald can I put into freezer immediately?

  8. Helen says:

    Any correlation between high lipase in breast milk and infant weight gain?

    Hi, I’ve just found your website and think its a really good resource. I was originally looking for information as to why my breast milk may be souring quickly but I have of course discovered its likely to be due yo high lipase content. However this got me thinking……if my milk is high in lipase and therefore breaks down more quickly whilst being stored does it also break down more quickly when baby digests it? Both my babies have struggled to gain weight in accordance with the published growth charts and I just wondered if there was any correlation between infant weight gain and high lipase in the breast milk they consume? i.e. because it breaks down more quickly, it take less time/effort for them to digest it and therefore they do not gain as much nutritional value from it or perhaps due to it’s high lipase content it’s actually lower in fat/ calories than milk that is not high in lipase and therefore baby’s weight gain is effected as a result.

    I have tried to research this but haven’t come up with much. I just though you may know the answer or have access to some resources that may provide an answer.

    Any assistance gratefully received.

    • Admin says:

      Hi Helen. I haven’t seen any research to support that conclusion, but it is an interesting theory. However, the lipase reaction happens when air hits the milk. That is why babies have no problem eating directly from our breast. Lipase, as you know, breaks down lactose. This is why it is impossible for breastfed babies to be lactose intolerant. We as humans only become “Lactose intolerant” once we are weaned. That being said I don’t know that it would have anything to do with how the baby breaks down the milk or digests. Poor weight gain often is a result of either low fat content in milk (this is more common in vegitarians or pescatarians due to the lack of high protein a salytic acid in their diet) or poor milk transfer. Milk transfer can be a result of an anatomical issue in the baby such as tongue tie known as ankoglossia, or torticollus from the baby’s neck, or simply not being latched deep enough onto the breast. In those cases baby has enough pees and poops, but is not gaining simply because the baby is burning more calories then they are taking in. If there is a foremilk/hindmilk imbalance that can result is slow weight gain as well. So to answer your question, I do not think there is a direct link between lipase and poor weight gain, but it certainly would be worth researching. I would be more then happy to put it out there in my community and see if I can find any more information for you. Great thought!! Thank you.

  9. Helen says:

    Thank you for your response and additional theories on why weight gain may be effected…..this has me asking more questions though (sitting down to breastfed, I have lots of time to think! 🙂 )

    My babies have both been exclusively breastfed but by two different methods – pumped then bottled for the first, actual breast for the second.

    The first was poorly when he was born, had to have surgery and was admitted to the neonatal intensive care for three weeks following his birth. During this time he lost 20% of his birth weight and struggled to regain his birth weight within this time frame. However, despite my theory that the antibiotics he had been given postoperatively may have effected his guts ability to absorb all the nutrient and gain weight. That and the fact he was poorly and weight gain was probably not his little bodies priority, healing itself was. Anyway, I was able to take him out of the incubator to feed him, which I did, night and day as I stayed at the hospital with him. Our feeding was observed by all the great feeding specialists and there was nothing they could find wrong with the latch, sucking etc and it was their view that his weight would come on it would just take time. However this was not the view of the other medical staff and I was, I felt, persecuted by them. I was accused of not producing enough milk and not producing good enough quality milk. They even had me feed the baby a minimal volume of milk and when I said he was showing signs of being full, they still made me give him some more because he hadn’t had the quota recommended and sure enough he was sick, brought up most of the feed and was upset. All of this was awful and terribly upsetting for me too – I just felt bullied and made to feel inadequate & at fault. It was truly heartbreaking! As if I wasn’t feeling bad enough anyway that my baby was born with a rare & unexplained condition that he developed only a few hours before birth. Anyway, determined to continue breast feeding, I ended up pumping to prove I was producing enough milk and bottle feeding to show how much he was taking on each feed. Slowly but surely after a couple of weeks, he started to gain some weight albeit not a the normal rate, and we were allowed to come home. However, he had got used to the bottle and would switch back to the breast. I pumped and exclusively breastfed him for 7months. Despite gaining weight more slowly that expected by the growth charts he did gain weight, he met and exceeded all of his milestones and I now have a very bright, articulate and lively 5 year old who continues to exceed expectation in whatever he does.

    With my second it has been much easier. She was born with no complications & able to come home within 24hours. Our breast feeding technique was assessed at the hospital and we were told we were doing fine. We’ve had a couple of blips with positioning in the early days that have led to a blocked duct and a cracked nipple but I have sought advice & we’ve quickly rectified this. However, she too is not conforming to the growth chart and gaining weight at the rate they want her too. However, she does enough pees & poops and developmentally she is as bright as a button. The only difference with this pregnancy is that I was diagnosed with type II diabetes just prior to it and take oral medication for it. My research has led me to believe that this won’t effect my milk and won’t transfer to the baby through my milk in any amount that would cause her metabolism to be effected in any way. Again, some professional have said things that have made me feel just terrible as they essentially accuse me of lying about how frequently she feeds and for how long. What they can’t dispute is her nappies and her development.

    So, two very different feeding stories but one mom. There have been no anatomical issues with either baby & I don’t believe I have IGT. So I am interested to know about fore milk/hind milk imbalance. I have wondered if this is possible and will tend to put baby back onto the same breast if she feeds for 10mins and then comes off as I’m conscious that my breast won’t have emptied and she isn’t likely to have got enough hindmilk.

    Also, rather interestingly her growth is not that dissimilar to my little boys was when you compare the two charts so perhaps there are some genetic factors at play that we cannot control?


    P.s I appreciate you offering to put my theory out to other too and potentially stimulate some further research.

    • Admin says:

      I so appreciate your theories, and all the thought you have put into this. It just shows what a great momma you are!! Your instincts are right on. You can’t dispute the babies output. If there are enough pees and poops then we know that the baby is ingesting the correct amount of ounces. However you bring up an interesting questions about foremilk/hindmilk imbalance. This is very rare, and the poops often are lime green, watery, almost soapy looking. If your baby is still having yellow seedy poop, it is unlikely that you are experiencing a foremilk imbalance. You are correct however that, that can lead to poor weight gain despite adequate amounts of diapers/nappies. One quick way to fix that is by first massaging the breasts prior to feeding. This helps “homogenize your milk if you will. The fatty part of the milk often sticks to your milk ducts. However, if you massage or shake your breasts prior to feeding it is as if you have mixed the milk, and then the baby will get all the hindmilk. Are you eating enough calories? Often we will see poor weight gain in mom’s who are not getting enough calories or enough protein. I had one case of a mom who only ate fish and veggies. No carbs, no good fats, no high protein in her diet. She made plenty of milk, was able to pump out 6 oz each breast, but the baby would not gain well. Despite having copeous amounts of nappies, there just wasn’t enough calories or fat/protein in her milk to put the weight on the baby. So that is something to consider. I know you mentioned you are a diabetic, so naturally you will be watching your caloric intake and your sugars. Make sure you are getting enough iron rich foods and protein. The medication should be fine, but you may just want to increase your feeds to every 2 hours in the day and every 4 at night. Also you have a very valid, and well documented, point about genetics playing a role. As long as her growth pattern is consistant, that she is continued to grow, her doctor should be fine. My kids are in the 5th percentile, always have been for their weight and height. It is just their genetic pool. If she is hitting her developmental milestones, then I wouldn’t worry too much. Best of luck and I hope this helps.

      • Helen says:

        That’s great thank you. Lots of yellow seedy poos, so that’s reassuring. I’ll keep an eye on my diet & calorific intake. For non-diabetic moms it’s a balancing act but with the diabetes you are even more conscious about balancing your diet for the long term health of both yourself and your baby. Post pregnancy hormonal changes can also make it difficult to get your diet just right too, particularly for diabetics I think. Without the right support, encouragement and knowledge/knowledgable professionals, it can be really off putting for any mom wanting to breastfed but for those type II diabetics it’s even harder, yet breastfeeding can be more beneficial overall to a type II diabetic mom’s health (and allows them a few more well deserved treats than normal too). Information and support on specialist diabetic websites is also very limited and often disappointing as it tends to focus more on the initial few days when milk can be delayed coming in etc. It upsets me that sometimes moms are treated and spoken too in such a way that it almost encourages them to “fail” and feel they have no choice but to switch to formula. To find someone offering potential solutions is a refreshing change in my experience.
        Thank you once again for your advice & support.

  10. Sara says:

    I know I have a lipase issue as I did with my first child but it didn’t seem to stop her from drinking it. But now I am worrying about my current nursing child, as I am getting ready to return to work. What will be an indicator that it doesn’t agree with her? Tonight I gave her a bottle from my freezer supply as I am trying to get her used to the bottle. She drank it slowly about 25 minutes for an oz. After that she seemed fine. But when I went to nurse her again before bed she threw up all over. She is not a baby that throws up usually. Would this mean that she is going to have issues with my frozen milk supply? If throwing up is a result after bottle feedings?

    Thank you.

    • Admin says:

      Not necessarily. I would try pumping directly into breastmilk bags, vs pumping into a bottle. This will allow less air to hit the milk which is what causes the reaction. Also try decreasing the amount of high fats in your diet as that can attribute to a higher lipase level. It also could have been just a fluke with that particular bag of milk. Hopefully things will get better for you! Best of luck.

  11. Jodi Blair says:

    I stumbled across your post in my tireless search for a “cure” to my recent discovery of high lipase in my milk. I am quite certain that this was the problem with my last baby as he would not take a bottle (I thought it was storage issues and gave up the bottle fight to EBF only to one year) but now we are having the same issues with out 7mo guy. I tasted my milk and it def has the funky taste that so many mention. I am resolved to get to the problem source for high lipase as I am stubbornly refusing to HAVE to scald after storage. You are the first person I have found that mentions there being a correlation between a high fat diet and higher lipase levels. Can you expound on that a bit more or show me some other info please? I am very curious about this as I am really hoping to “fix” this. Thanks!!

    • Admin says:

      I am glad you found this info helpful. You can also try pumping directly into a bag vs. a bottle. Less air will hit the milk that way. Basically high fat content needs to be broken down more, thus resulting in a stronger lipase reaction. I recommend eating more protein, increasing your water intake, and decreasing the bad fats, and replace with good fats like avocado, almonds etc. I will send you some more information on the subject as well. Best of luck!

  12. Erin says:

    I have been pumping and storing for five weeks and just defrosted some milk for the first time. I think it may have a lipase issue due to odor and I have also noticed some soapy looking bubbles while pumping occasionally. If the baby won’t take the thawed milk, will scalding after thawing help at all? Thanks for any thoughts you have.

    • Admin says:

      There haven’t been any reports or studies about scalding the milk after defrosting, if that will help take away the lipase reaction. The milk itself is okay to feed the baby, it just causes a bitter taste. That being said I would have to research more on whether scalding post freezing will help. I will keep you appraised of what I find.

  13. Kasey says:

    Hi! Can you scald breast milk after it’s been frozen?
    It’s the 2nd time this has happened to me and with my first child I ended up throwing out over 350 ounces of soured breast milk, (it was sour after thawing it from freezer). I was devastated. I have about 35 ounces in our deep freezer now and the first bag I thawed is sour and rancid tasting. I am wondering if I can scald it once it has been thawed??
    Please help me!!
    Also, what are the scalding guidelines? I read in an earlier post about dipping scalded milk into ice water. Can you explain the process so I will get it right 🙂 what type of container do you recommend putting the milk in right after scalding to go into ice bath? Do you pour it immediately into the bottle then dip bottle in ice bath?
    Agggghhhh I hate that we all have problems with this.
    Thank you for all your help!! God bless,

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