Breast milk contains antibodies and live white blood cells that help your baby fight against infection. And, when you or your baby are sick, the amount of these cells in your breast milk increases.


Before we dig down to the main thing, let's clear some things up.

What is the immune system[1]?

-The immune system is a collection of cells and proteins that works to protect the body from harmful microorganisms, such as bacteria, viruses and fungi.

-Immunity is a state of protection against disease through the activities of the immune system."

We have three types of immunity, which works as a defence in preventing diseases from entering the body[2]:

1. Innate Immunity (natural immunity)

The one that we are born with - cough reflex, enzymes in tears and skin oils, mucus, which traps bacteria and small particles, skin, stomach acid.

2. Adaptive Immunity (active immunity)

This is immunity that develops with exposure to various antigens. Your immune system builds a defence against that specific antigen.

3. Passive Immunity

The protection you can get from someone else. It provides immediate protection against an antigen but does not provide long-lasting protection. Infants have passive immunity because they are born with antibodies that are transferred through the placenta from their mother. You can get it also from injection of antiserum, which contains antibodies that are formed by another person or animal (for example immune serum globulin (given for hepatitis exposure) and tetanus antitoxin).

So, we won't dig in depth of immune system for now. But we've built a base to a better understanding of what we will talk about below.


It starts in the womb (at the last three months of pregnancy). During pregnancy, the mother's immune system produces antibodies (immunoglobulin g =IgG*), which are transported across the placenta to fetus's blood supply[3]. IgGs are the most common type of antibody in our bodies (we have five types of Ig in our bodies)[4].

As you already know, passive immunity does not provide long-lasting protection. Therefore, a baby's system is »protected« with it just a limited amount of time. That said, these maternal antibodies (IgG's), start to wane after a few months and disappear at the age of 12 months[5]. But, that's not the end of the story.

Babies can also get passive immunity through breast milk.

Human milk protects the baby against infections mainly via the secretory IgA antibodies (not IgG, as we've previously discussed). The milk of mothers who give birth prematurely contains higher amounts of phagocytes and secretory immunoglobulin A. In the full-term newborn gut, plasma cells responsible for producing IgA are absent for about 10 days after birth, and it takes up to 30 days postpartum for the neonatal intestine to produce levels of IgA that are sufficient for protection[6].

So, what do IgA antibodies do?

They work inside the baby's gastrointestinal tract, so that they penetrate and protect the mucous membranes in the baby’s mouth, airway, throat, and intestines[7]. A fully breastfed infant receives as much as 0.5-1 g of secretory immunoglobulin A (IgA) antibodies daily[8].

But it's not just IgA's. There are also several other factors included in human milk that contribute to the protection.

These are lactoferrin, lysozyme, casein, cytokines, chemokines and also leukocytes and triglycerides.[9]

However, those only protect against infection through their digestive tract; it does not provide bloodstream antibodies (as IgG’s does) to protect against various illnesses. Moreover, this passive (IgA) immunity continues until a baby is weaned. Since passive immunity (from IgG's and IgA's) is temporary, and breastfeeding antibodies can only protect infant within the GI tract while breastfeeding is occurring.

With low levels of IgG's at six months, infants immune system have already begun to mature. If the infant is healthy, he's producing his own antibodies (igG's) from the germs they encountered in their environment. And this is what we call active immunity. The type of immunity that the body develops only after we've been exposed to a virus or germ[10].


As you can see, the interaction between mother and baby through breastmilk plays a vital role in the development of baby’s immune system. Evidence from human and animal studies indicates that antigen in breast milk can impact actively a child's immune reactivity in both the short and long term[11].

There’re some studies with positive outcomes, regarding enhanced protection remaining for years after breastfeeding against diarrhoea, respiratory tract infections, otitis media, Haemophilus influenza type b infections, and wheezing illness. In several instances, the protection seems to improve with the duration of breastfeeding. There's also suggestions of protection against immunologic diseases (like coeliac disease and possibly allergy ) and even autoimmune diseases and tumours [12].

But we need further confirmation on this. While the industry is constantly trying to improve infant formula by adding fatty acids, oligosaccharides, lactoferrin ect., human milk has such a far-reaching effect on an infant's immune system and development.

Therefore, if you have an option to breastfeed, be encouraged to breastfeed for up to six months AT LEAST and beyond to promote the best health for your child.


[1] Association, BMA-British Medical. Illustrated Medical Dictionary. 4th edition. London: DK, 2018.

[2] Immune response: MedlinePlus Medical Encyclopedia. (n.d.). Retrieved from

[3] Hanson, L. A. (2007, August). Session 1: Feeding and infant development breast-feeding and immune function. Retrieved from

[4] Antibody. (2018, November 22). Retrieved from

[5], [10] Niewiesk S. (2014). Maternal antibodies: clinical significance, mechanism of interference with immune responses, and possible vaccination strategies. Frontiers in immunology, 5, 446. doi:10.3389/fimmu.2014.00446

[6] Xanthou, M., Bines, J., & Walker, W. A. (n.d.). Human milk and intestinal host defense in newborns: An update. Retrieved from

[7] Hanson, L. A., & Söderström, T. (n.d.). Human milk: Defense against infection. Retrieved from

[8] Hanson, L. A., Hahn-Zoric, M., Berndes, M., Ashraf, R., Herias, V., Jalil, F., . . . Mattsby-Baltzer, I. (1994, October). Breast feeding: Overview and breast milk immunology. Retrieved from

[9] Jakaitis, B. M., & Denning, P. W. (2014). Human breast milk and the gastrointestinal innate immune system. Clinics in perinatology, 41(2), 423-35. Retrieved from

[11] Verhasselt V. (2015). Is infant immunization by breastfeeding possible?. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 370(1671), 20140139.

[12] Hanson, L. A. (1998, December). Breastfeeding provides passive and likely long-lasting active immunity. Retrieved from