Can You Mix Breast Milk And Infant Formula?

Combining Breast Milk And Formula In The Same Bottle.
Can you mix breast milk and formula?. Floortje/E+/Getty Images

Can You Put Breast Milk and Formula In The Same Bottle?

If you're supplementing your baby, you may have to give your child breast milk and infant formula in the same feeding. But, can you put them both into the same bottle?

Yes, it's technically OK to mix your breast milk with an already prepared infant formula in the same bottle. However, even though it is more convenient to combine them, it is better if you can offer them one at a time.

There are two good reasons to give formula and breast milk separately.

1. If you offer your breast milk first, your baby will get all of your breast milk, and you won't have to worry about wasting the little bit of breast milk that you have. But, if you add your breast milk to a bottle of infant formula, some of your breast milk will go to waste if your baby doesn't finish the entire bottle.

2. Since breast milk contains more nutritional and health properties than formula, it is best if your baby gets all of the breast milk that's available. Then, once your child finishes your breast milk, you can offer the formula supplement for the remainder of the feeding.

Can You Mix Infant Formula With Breast Milk Instead Of Water?

When you buy formula for your baby, you will usually get one of these 3 types: ready-to-feed, concentrated liquid, or powdered. If you decide to add your breast milk into a bottle of ready-to-feed formula that is OK.

It will not harm your child. It's also fine if you properly mix the concentrated liquid or powdered formula with the correct amount of water according to the directions on the container, and then add your breast milk.

However, you should NEVER add undiluted powdered infant formula or concentrated liquid formula directly into your breast milk, and you should NEVER use your breast milk in place of water to mix concentrated or powdered infant formula.

Preparing Concentrated Liquid And Powdered Infant Formula

If you use concentrated liquid formula or powdered infant formula, be sure to make it according to the manufacturer's instructions or any alternate instructions that your baby's doctor gives you. Concentrated and powdered infant formulas are typically diluted with sterile water for mixing formula, or safe drinking water that has been boiled for 5 minutes and then cooled. Depending on the quality of the water in your area and your baby's health, you may be able to use tap water. Talk to your child's doctor to find out if it's a safe alternative. 

The Danger Of Mixing Formula Directly Into Breast Milk

Infant formula is made to provide your baby with a specific amount of calories and nutrients in a specific volume of fluid.  For example, a standard formula is 20 calories per fluid ounce.  So, if you prepare the formula as directed, your baby gets the expected amount.  But, if you add powdered formula or concentrated liquid formula directly into your breast milk before you dilute it with water, it changes the balance of nutrient and water in both your breast milk and the infant formula.


When your baby is an infant, his kidneys are not yet mature. The kidneys of newborns and young infants need enough water to process all of the nutrients in their feedings, especially the proteins and the salts. When a feeding is too concentrated, it can be dangerous and just too much for your baby's little body to handle. Therefore, when preparing your child's formula, you should always use the correct amount of water and follow all the instructions that you are given.   

If you have any questions or concerns about how to dilute or mix your baby's formula correctly, call your baby's doctor.  


American Academy of Pediatrics. New Mother's Guide To Breastfeeding. Bantam Books. New York. 2011.

Lawrence, Ruth A., MD, Lawrence, Robert M., MD. Breastfeeding A Guide For The Medical Profession Seventh Edition. Mosby. 2011.

Perry, Shannon E., Marilyn J. Hockenberry, Deitra Leonard Lowdermilk, and David Wilson. Maternal Child Nursing Care. Elsevier Health Sciences. 2014.

Riordan, J., and Wambach, K. Breastfeeding and Human Lactation Fourth Edition. Jones and Bartlett Learning. 2014.

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