Breast Milk: Answers to the Common Questions

Definition, Stages, and Information About Human Breast Milk

Mother breastfeeding baby girl at home in New York City
What is breast milk?. Andria Patino/Corbis/Getty Images

What Is Breast Milk?

Breast milk is a liquid source of food made by a mother's breasts for her children. It's created in response to pregnancy and the suckling of a baby at the breast. Breast milk provides a child with complete nutrition, as well as protection against infections, diseases, and illnesses. Breastfeeding benefits mothers and children in a variety of ways, and many of the health benefits continue long after breastfeeding has ended.

What's in Breast Milk?

The composition of breast milk is complex. It consists of over 200 different substances, including protein, fat, carbohydrates, vitamins, minerals, other nutrients, enzymes, and hormones. This composition is not constant. It's different from mother to mother and even varies within the same mother. Breast milk also changes during each feeding, throughout the day, and over time to meet the needs of a growing child.

What are the Stages of Breast Milk?

The production of breastmilk begins in pregnancy, and it has three stages: colostrum, transitional breast milk, and mature breast milk.

Colostrum: Colostrum is the first breast milk. It's present at the end of pregnancy and during the first few days after the birth of your baby. It's usually thick, yellow and sticky, but it can also be thin and white or orange in color. Colostrum is easy for newborns to digest. It's high in protein, low in fat, and contains a high concentration of antibodies, specifically Immunoglobulin A (IgA), as well as white blood cells, to fight off infections.

It's also a natural laxative that helps prevent jaundice by clearing your baby's body of meconium: the first thick, black, tarry poop. The amount of colostrum that your body makes is small, but that small volume contains everything your new baby needs in the first few days of life.

Transitional Breast Milk: Transitional breast milk is a combination of colostrum and mature milk.

When your breast milk begins to “come in” at approximately 3 to 5 days after delivery, it mixes with the colostrum and gradually transitions to mature milk over the course of a few days or a week.

Mature Breast Milk: Your milk will change over to mature breast milk by the time your baby is about two weeks old. Mature brest milk is a combination of foremilk and hindmilk. When your baby latches on to nurse, the first milk to flow out of your breast is foremilk. Foremilk is thin, watery, and lower in fat and calories. As you continue to breastfeed, the hindmilk will follow. Hindmilk is thicker, creamier, and higher in fat and calories.

What Color Is Breast Milk Supposed to Be?

The colors of breast milk can change throughout the day, or from one day to the next. It's usually white, yellow, or bluish—but depending on what you eat, it could have a green, orange, brown or pink tint. Occasionally, blood from rusty pipe syndrome or cracked nipples can appear in your breast milk. It may be scary, but it isn't dangerous. As long as your baby is not refusing the breast, it's safe to continue to breastfeed if your milk changes color.


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

American Academy of Pediatrics. Your Baby's First Year Third Edition. Bantam Books. New York. 2010.

Lawrence, Ruth A., MD, Lawrence, Robert M., MD. Breastfeeding A Guide For The Medical Profession Sixth Edition. Mosby. Philadelphia. 2005.

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