Q: Our 4-month-old keeps getting white patches on her tongue. What is this?
A: It could be yeast, also known as thrush, a fungus that grows in warm, moist areas such as a baby's mouth or diaper area. It also can be found on a breastfeeding mother's nipples. One of the best ways to diagnose yeast is to try gently scraping it off with your fingernail; leftover milk will come off fairly easily, while yeast can't be scraped off. My first-line natural approach is to use 10 drops of grapefruit-seed extract per ounce of water. Apply this to your baby's tongue and, if you're breastfeeding, to your nipples every two to three hours for at least a week. If this doesn't work, see your pediatrician for medication.