When mum Ashlee Chase pumped milk for her baby Elliot only to discover it was a bright yellow colour, she wondered what on earth was going on. Her seven-year-old daughter Peyton home from school with a fever and throat infection, the mother-of-two thought she was simply coming down with the same virus.
"I read before that your milk could change for different reasons, but I was so sleep-deprived that morning, I just thought there was something wrong with it," Ms Chase told Yahoo Lifestyle.
But when she called her baby's pediatrician, she was told the reality was quite the opposite. Apparently, her breast milk's yellow hue signalled that there was more fat and antibodies in it to help baby Elliot fight the infection. And, incredibly, it is backwash from the baby feeding that lets mum's body know to produce the infection fighting milk.
Speaking to Yahoo Lifestyle, lactation consultant Leigh Ann O'Connor, explained some of the baby's saliva (in this case, containing the infection) goes into the a mother's breast during feeding.
"The baby's saliva goes back into the breast and then the breast manufactures special milk to protect the baby. This is one of nature's beautiful tricks to protect the offspring and to keep the population healthy and growing."
And it worked.
"The illness knocked my 7-year-old out for a week, but the baby only got a runny nose and a slight fever the night before I noticed the yellow," Ms Chase said.
Tired of copping criticism for continuing to breastfeed her baby, ("she's too old, she's just using you as a pacifier"), the mum took to Facebook to share pictures of the yellow milk, alongside her usual milk, to share exactly why she's still nursing her bub.
"100% why," Ms Chase wrote, explaining that the milk at the top was from three days prior when her baby was healthy. "Bottom [milk] is from today, after sick Elliot with a fever comfort nursed all night."
If you're interested in the science behind it - because it's pretty amazing - then allow me to break it down in a little more detail.
A 2013 study from The University of Western Australia, published in the journal Clinical and Translational Immunology, revealed that infections in both mums and bubs stimulate a rapid response of leukocytes (a type of white blood cell that helps fight infections) in breast milk.
In fact, colostrum, the liquid gold milk mums produce first, has even higher numbers of leukocytes (around 13 -70 per cent of total cells) for those precious early days. While the level of leukocytes then decreases over the next one - two weeks after bub is born, (to as little as 0-2 per cent of the composition of breast milk) the research showed that if either mum or baby develop an infection, these leukocytes increase again - to up to 94 per cent of the total cells in breast milk.
The researchers noted that while the mechanism behind the "leukocyte movement into the breast" when a baby is unwell remains unclear, there are some theories. If mum is exposed to bub's infection, this may then stimulate an immunological response which affects breast milk leukocyte content. And all this can happen via breastfeeding.
"During a milk ejection, duct pressure increases," the authors explain, "milk ducts dilate and milk flows toward the nipple/baby's mouth." As the hormone oxytocin (sometimes called the "love hormone") wears off, duct pressure decreases, milk ducts reduce in size and milk flows backwards - most likely together with saliva from the baby's mouth.
This is when researchers think microorganisms from a sick bub are then transferred back into the boob (probably during a pause in suckling), which then stimulates a local immune response.
Aren't our bodies incredible?