Immunoglobulins (Antibodies) in Breast Milk

Baby drinking milk from a bottle

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Immunoglobulins are antibodies. They're proteins that are made by your immune system after exposure to an antigen (something harmful to your body that causes an immune response). Immunoglobulins fight off germs, illness, and disease. They circulate throughout the body and can be found in blood, sweat, saliva, and breast milk

Secretory IgA in Breast Milk

Secretory immunoglobulin A (IgA) is the main antibody found in breast milk, and it's considered the most important one. Babies are born with low levels of IgA. As they grow, their immune system makes more IgA and their levels slowly rise. But when a baby breastfeeds, they get high levels of IgA from breast milk.

IgA is important because it coats and seals your baby's respiratory and intestinal tract to prevent germs from entering their body and ​bloodstream. The IgA antibodies can protect your child from a variety of illnesses including those caused by bacteria, viruses, fungi, and parasites.

Other Immunoglobulins

Besides IgA, there are four other types of immunoglobulins in breast milk: IgE, IgG, IgM, and IgD. Colostrum, the first breast milk, has very high levels of immunoglobulins, especially IgA. These antibodies fight off illness and infection, but they also protect against allergies, eczema, and wheezing, especially for infants who have a family history of allergies.

As your breast milk changes from colostrum to transitional milk and finally to mature breast milk, the concentrations of immunoglobulins change. However, even if you breastfeed for a year or longer, these immune properties can still be found in your breast milk.

Immunoglobins will continue to protect your child for as long as they breastfeed. And your child will continue to benefit from the immune-boosting substances in your breast milk long after breastfeeding has ended.

While we do not know everything that these immunoglobulins do, we are learning more and more about them all the time. And while it is safe and nutritious, infant formula cannot duplicate these properties of breast milk.

Benefits for Premature Babies

A premature baby's immune system is not as strong as the immune system of a full-term baby. Preemies are at greater risk of getting infections, and have a harder time dealing with them than full-term infants. That's why breast milk is so important for premature babies. The antibodies in breast milk will help your preemie to fight off bacterial and viral infections.

Benefits for Babies in Day Care

Babies who are cared for in a group setting can benefit from breast milk. The antibodies in the breast milk that you pump for your child can help protect them from many of the common childhood illnesses that can be easily picked up in a childcare setting.

Breastfed babies are less likely to get gastrointestinal illnesses that cause diarrhea and vomiting. They also have a lower rate of respiratory infections and ear infections when compared to children who receive formula.

Pumping and Storing Breast Milk 

When you pump your breast milk, some of the bacteria and germs on your skin can get into your breast milk storage container along with your breast milk. The immune factors in breast milk help to prevent this bacteria from growing and causing your baby to become ill.

If you pump, it's ideal to give your baby fresh breast milk. However, that's not always realistic. So it's important to follow the safety guidelines for the collection and storage of breast milk.

  • Breast milk stored in the refrigerator maintains most of its immune properties.
  • Heating breast milk at high temperatures (especially in the microwave—which is not recommended anyway), can destroy the antibodies and other immune factors in your breast milk.
  • When you freeze breast milk, it loses some of its healthy immune factors, but not all.

When You or Your Baby Are Sick

If you catch a cold or develop an illness while you're breastfeeding, you can usually continue to breastfeed. Breastfeeding through most of the common illnesses is safe. By the time you realize you're sick, it's likely that your baby has already been exposed to your illness.

As you continue to breastfeed, you pass the antibodies that your body is making to fight off your illness to your baby through your breast milk. Your child may be able to fight the illness easier or may not even catch it.

If your baby is sick, the antibodies in your breast milk will help your baby to fight off the illness or infection they have developed. In addition to antibodies, breast milk provides nutrition, fluids, and comfort to sick children.

The Immune System and Vaccination

While breast milk provides your baby with important immune protection, it does not protect your baby from all the diseases that they may come into contact with during their lifetime. And many dangerous and deadly illnesses are preventable through childhood immunizations.

Vaccination is safe and vital to your child's health. Vaccines save millions of lives each year. Misinformation leads some people to question their efficacy, but these beliefs are not backed by credible research.

If you have any questions or concerns about your baby's health, breastfeeding, or vaccinations, discuss them with your child's healthcare provider. Your baby's doctor will provide you with a schedule of recommended vaccines for your child at each developmental stage. 

7 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. KidsHealth from Nemours. Breastfeeding vs. formula feeding.

  2. Palmeira P, Carneiro-Sampaio M. Immunology of breast milk. Rev Assoc Med Bras. 2016;62(6):584-593.  doi:10.1590/1806-9282.62.06.584

  3. Centers for Disease Control and Prevention. Proper storage and preparation of breast milk.

  4. Academy of Nutrition and Dietetics. Keeping breast milk safe.

  5. Kourtis AP. Keeping Your Child Healthy in a Germ-Filled World: A Guide for Parents. Johns Hopkins University Press. 2011.

  6. Orenstein WA, Ahmed R. Simply put: Vaccination saves livesProc Natl Acad Sci U S A. 2017;114(16):4031-4033. doi:10.1073/pnas.1704507114

  7. Centers for Disease Control and Prevention. Immunizations and developmental milestones for your child from birth through 6 years old.

Additional Reading
  • American Academy of Pediatrics. New Mother’s Guide to Breastfeeding. Bantam Books, 2011.

  • Lawrence RA, Lawrence RM. Breastfeeding A Guide For The Medical Profession Seventh Edition. Mosby, 2011.

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

By Donna Murray, RN, BSN
Donna Murray, RN, BSN has a Bachelor of Science in Nursing from Rutgers University and is a current member of Sigma Theta Tau, the Honor Society of Nursing.