If you’re a pumping mama, the journey breast milk takes from breast to baby is often filled with pit stops. And if one of those stops is the fridge or freezer, it’s important to learn how to warm breast milk safely and effectively.
Why You Should Warm Up Breast Milk
You can give baby cold breast milk—it’s perfectly safe to do so—but, because breast milk usually comes straight from mom, babies are used to lukewarm, body temperature milk.
Another reason to learn how to warm breast milk is energetics, or the way the temperature of food affects the way it’s digested. In general, room temperature and warm foods are thought to be easier to digest and are more nourishing than cold foods. So warming breast milk would, in theory, make it easier for baby to digest.
What is the Ideal Temperature to Warm Breast Milk?
Once warmed, gently swirl breast milk and squeeze a few drops onto the inside of your wrist to test the temperature. It should feel relatively neutral against your skin—it should not feel cold, and it should not feel hot. Though I don’t expect you to take out a food thermometer, the below temperature ranges may help guide you:
32 to 78º F: It’s safe to feed baby milk within this temperature range, but it may not be as optimal for baby’s digestion or taste preferences. In fact, some babies may flat out refuse milk this cold.
98.6º F: This is generally considered the average normal body temperature. It’s a good target when warming breast milk, since it echos the temperature of milk coming directly from mama’s breast. Plus, it’s not hot enough to destroy any of the nutrients or pre/probiotic qualities of breast milk.
99º to 105º F: This temperature range is still considered lukewarm, so although it is slightly higher than the recommended temperature for breast milk, it’s not hot enough to destroy the nutrients or pose a danger to baby.
106º F and up: Heating breast milk beyond lukewarm temperatures is not recommended. Hot liquid can burn baby’s mouth, plus studies show the quality of breast milk deteriorates when heated beyond recommended ranges. (More on that below!)
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How to Warm Breast Milk
Now that you know the why, it’s time to tackle how to warm breast milk. There are actually 4 different ways to warm breast milk safely, and in a way that preserves the nutrients.
#1: Running Water Method
Step 1: Run warm, not hot, tap water
Step 2: Place a closed bottle or bag of breast milk under the running water
Step 3: Rotate the container slowly for a few minutes until the contents are warm
Step 4: Swirl to mix gently
Step 5: Test the temp by placing a few drops on your wrist before giving to baby
While this method of how to warm breast milk is effective, it’s not the most environmentally friendly. When possible opt for a method that uses standing warm water or no water at all (like the methods below), so less water gets wasted.
#2: Warm Water Bath Method
Step 1: Fill a bowl with warm water
Step 2: Place a closed bottle or bag of breast milk in the container of warm water for a few minutes
Step 3: Swirl to mix gently
Step 4: Test the temp by placing a few drops on your wrist before giving to baby
#3: Countertop Method
Step 1: Place a closed bottle or bag of breast milk on the countertop until it reaches room temperature
Step 2: Swirl to mix gently
Step 3: Test the temp by placing a few drops on your wrist before giving to baby
Though many moms leave breast milk out for much longer (up to eight hours!) with no issues, the official recommendation is not to leave breast milk out for longer than two hours. This is especially important for preemies and babies with compromised immune systems. (source)
#4: Bottle Warmer Method
To learn how to warm breast milk with a bottle warmer, follow the instructions on your own device (instructions vary based on manufacturer)—but be careful with this one. It’s easy to overheat breast milk in a bottle warmer, which poses obvious dangers to baby, but could also destroy some of the living nutrients. (More on that below!)
How Not to Warm Breast Milk
Breast milk isn’t just a mix of micro and macronutrients—it’s also teeming with “live” components. Breast milk is so special, because it’s full of bacteria-fighting, immune-supporting, microbiome-building, and digestion-enhancing cells, enzymes, and probiotics.
Breast milk composition
And research suggests overheating breast milk can damage or destroy some of these live components and heat-sensitive nutrients. One study found that high temperatures can reduce folate levels in breast milk by as much as 24 percent! Another study shows that warming milk above 143º F can also destroy the beneficial probiotic bacteria and white blood cells in breast milk. While that sounds hot, the tap water in may households can reach 140º F or more. (source)
They call breast milk liquid gold for a reason—you want to be sure to preserve all of those powerful nutrients by learning how to warm breast milk properly.
Follow these two rules to help prevent overheating:
Rule # 1: Never Use a Microwave to Warm Breast Milk
You never, ever want to reheat breast milk in the microwave. (source)
Because microwave ovens don’t heat liquids evenly, hot pockets of liquids can develop. And those hot spots can burn baby’s delicate mouth. Plus, research suggests bottles that get too hot can explode, causing second-degree burns.
Rule #2: Make Sure the Water Isn’t Too Hot
Don’t use boiling water (or even hot tap water for that matter) to warm breast milk. Doing so could lead to overheating. One study suggests heating bottles to 120º F causes the quality of breast milk to deteriorate significantly. Lukewarm water (generally between 98º and 105º F) is enough to warm breast milk to body temperature—exactly what it should be!
Rule #3: Don’t Put Breastmilk Directly Into a Pan and Heat
First off, this can expose breast milk to more bacteria and outside influences. Secondly, it is very hard to control temperature this way. You risk overheating, which can not only damage milk quality, but also pose a danger to baby.
How Long is Heated Breast Milk Good For?
While freshly pumped and expressed milk can be left at room temperature for as long as 6-8 hours (4 hours in a particularly warm room), heated milk that was previously refrigerated or frozen has a shorter shelf life. Once milk has been warmed to room temperature, safety guidelines say you should use it within 2 hours.
Keep in mind that many moms leave warmed breast milk out for longer and don’t have any problem—the recommendations err on the side of caution. This is just the safest option, particularly if baby has a compromised immune system.
Because of this small window, it’s a good idea to store, thaw, and warm breast milk in small amounts. Try to store two to four ounces of milk per bag or bottle. (This is helpful for paced bottle feeding, anyway!) Then, only thaw and warm what you’ll use to prevent waste. You can always heat up more!
Can I Reheat Breast Milk That Was Already Heated?
If you can, it’s best to avoid feeding baby leftover milk. Once baby drinks from the bottle, it is possible that his/her saliva can introduce bacteria into the breast milk. But breast milk is liquid gold, and some mamas just can’t bear to see it go to waste. Some experts say the risk is low and studies show that the antibodies in breast milk help fight any potential bacteria.
Again, it’s best to store and feed breast milk in small amounts to avoid this problem altogether. And, if you do use leftover breast milk, be sure to use it within a few hours. Talk to your healthcare provider about what’s best for your child.
Note: For some babies—a child with a compromised immune system such as a preemie or a sick infant—rewarmed milk is not a good idea at all. In these cases, it’s safest to discard any unused breast milk.
Can You Refrigerate a Bottle After It’s Been Warmed?
As noted above, warmed breast milk should be consumed within two hours.
Some mamas prefer to leave the bottle on the counter, so they don’t need to reheat it. Other mamas prefer to refrigerate the milk.
The choice is yours, but it’s a good idea to refrigerate any unused breast milk, particularly if you’re outdoors or the room is hot and/or sunny.
Breast milk is amazingly resilient, but that doesn’t mean it never goes bad. While it can sit out for longer than you might expect, it can spoil.
Some signs of spoilage include:
- A foul smell
- A strange taste
- A change in texture or color
- Separation that refuses to mix when swirled together
Many food safety experts live by the saying, “when in doubt, throw it out.” If you’re unsure about whether or not your stored breast milk is safe to serve, toss it. It’s always better to be safe than sorry!
How About You?
Do you warm your expressed or pumped breast milk before giving it to your baby? How does your baby prefer breast milk?