The Bacteria In Your Breasts

Is this the reason why breast-feeding wins out over formula?

We’ve long known that breast-feeding is recommended over formula feeding when possible, and leads to more robust babies. Could bacteria be at least partially responsible for this advantage? Photo by Wes Hicks on Unsplash

One of the most impactful lessons that I’ve learned, over and over, as a microbiome scientist is that there are bacteria everywhere and in everything.

Very few things are totally sterile.

• Your mouth? Definitely not sterile, even immediately after you gargled with Listerine.
• The dry, dusty floor of a classroom or office room? Teeming with bacteria.
• Many of us know that the human intestinal tract is filled with bacteria, but some of them even survive in our acid-filled stomach.
• Urine? Nope, that myth is incorrect, and it’s not sterile.

But what about something like breast milk? Barring any contamination from the skin (which is also teeming with bacteria, no matter how many showers you take), shouldn’t that be sterile?

After all, newborn infants are fragile, with weak immune systems that haven’t had time to fully develop. Shouldn’t we evolve to keep them safe and protected from bacteria?

Not the case. Breast milk, as reported in several studies, is teeming with a number of different species of bacteria.