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The Immunological Power of Breastfeeding during Illness

February 19, 2025

Breastfeeding is a dynamic process. The contents of your breastmilk change as your baby grows older, from colostrum to transitional milk to mature milk. Each day the components of your milk change from morning to night and from the start of a feed to the end of the feed. One amazing way in which your breastmilk changes is when you or your child is ill.

In general, milk contains immunologic properties that benefit your child. Breastfed babies have decreased rates of infectious diseases including respiratory infections, GI illnesses, ear infections, etc.

When you are ill, your milk changes to contain more white blood cells (leukocytes) and antibodies (mostly secretory IgA and some IgG) specific to your illness that are passed on to protect your baby. 

What about when you are well but your child is ill?

When your child feeds at the breast, some milk (and likely saliva from your baby's mouth) flows back into the breast. This is called retrograde ductal flow, but is essentially backwash. It is thought that when your child is sick, this backwash contains pathogens that stimulate a local immune response in the breast to start making antibodies specific to these particles. This quickly alters your milk so that it contains white blood cells and antibodies that match the pathogen your child is infected with to help fight off the infection.

This is personalized medicine at its best!

Take Home Points:

1. When you are ill, it is often beneficial to continue to breastfeed or provide your child with breastmilk as your milk may contain white blood cells, antibodies, and other immunologic properties to protect your child from the illness if your child was already exposed.*

2. When your baby is sick, directly feeding at the breast provides more than nutrition and comfort, it acts as personalized medicine for your baby. If you have to pump, always provide the freshest milk possible because it has the most nutrients and the most relevant immunologic profile for your baby.

*Caveat: There are a few illnesses in which breastfeeding is contraindicated, including: HTLV1, HTLV2, ebola virus, untreated brucellosis, or mpox virus.  Lactating people with HIV, shingles, HSV sores on the breast, TB, measles, or chicken pox should discuss with their physicians.  Some infections that spread through air or contact may require separation of mom and baby, during which mom should continue to express milk to be given to the baby by another caregiver. 

**Please keep in mind that every family and illness may warrant different management.  Please discuss with your doctor regarding your own personal situation.**

Citations:

https://www.cdc.gov/breastfeeding-special-circumstances/hcp/contraindications/index.html

Hassiotou F, Hepworth AR, Metzger P, et al. Maternal and infant infections stimulate a rapid leukocyte response in breastmilk. Clin Transl Immunology. 2013;2(4):e3. Published 2013 Apr 12. doi:10.1038/cti.2013.1

Lokossou GAG, Kouakanou L, Schumacher A, Zenclussen AC. Human Breast Milk: From Food to Active Immune Response With Disease Protection in Infants and Mothers. Front Immunol. 2022;13:849012. Published 2022 Apr 5. doi:10.3389/fimmu.2022.849012