It’s kind of gross to talk about, but you can learn a lot from snot. While mucus may be a bit of an annoyance, it plays an important role in your child’s body. Mucus lines organs with a protective layer, keeping dust and dirt out to help fight off infections. But not all mucus is the same. Different colors can mean fungal infection or other serious health issues. And mucus from allergies is different from that of the common cold. Pediatrician Cindy Gellner, MD, explains what the different colors of mucus coming out of your child’s nose really mean, and when you should visit the doctor.