Every breastfeed is a gift of millions of protective living cells

You have thousands of living cells in each millilitre of your mature milk (and lots that are dead, too, but which still continue to strengthen your baby's immune system). I'm not talking here about the live organisms which make up your milk microbiome, but about the powerful protective cells which are made by your own body. Some come from your blood, some come from your breast tissue. This is quite different to commercial milk formula, for instance, which doesn't include any viable cells.

As usual in biological systems, there are very high levels of variability in milk cell numbers between you and other women, and also from day to day in your own milk, and one is ‘healthier’ than the other. Milk cell numbers also vary throughout the different phases of your milk-making.

Three kinds of cells from your body inhabit the living tissue of your milk.

1. Cells from the lining of your milk glands and ducts

Ninety-eight percent of the living cells found within your milk are lactocytes and myoepithelial cells which have been discarded from the constantly renewing alveoli and ducts. They continue to make and secrete milk proteins and other factors, and interact to strengthen your breasts' immune responses inside your milk.

2. Immune cells

A fluctuating number are cells from your blood, in particular the white cells known as leucocytes. Each millilitre of your milk contains perhaps 260,000 leucocyctes.

• White cells from your blood and lymphatic vessels migrate into your milk through the tight junctions between your lactocytes or milk-making cells. They protect your baby by regulating baby's immune response, and they also produce a range of bioactive substances.

• If you have a breast inflammation such as nipple pain, blocked ducts mastitis or abscess, or if your baby has an infection, your leucocyte numbers dramatically increase. For instance, in mastitis,leucocytes increase from 2% to up to 95% of your milk cells! During periods of infection of either mother or infant, number of protective leucocytes your baby ingests daily can reach billions!

3. Stem cells

Your baby receives a powerful stem cell transplant from your own body many times a day, when you're breastfeeding!

Up to six percent of the cells inside your breast milk are stem, which travel into your baby's gut to strengthen your baby's immune system, and which also have the capacity to repair tissue inside your own breast by turning into lactocytes and myoepithelial cells.

Amazingly, stem cells are found in the milk you make for your toddler if you continue to breastfeed, two to four years after you gave birth!