A: If your baby's poops become loose, watery, and more frequent than usual, a stomach virus is a probable culprit. A rotavirus infection, particularly common during winter months, is the most common cause of severe diarrhea (lasting about 10 to 12 days) in kids under 2 and is easily spread via dirty hands or toys. A milk or food allergy, changes in a nursing mom's diet, excessive juice intake (particularly apple or pear), and certain antibiotics can also trigger diarrhea. Call your doctor if your baby has watery stools for more than three days (immediately if he's younger than 3 months), if diarrhea is accompanied by vomiting, or if you see blood in his stool. Replace lost fluids with an oral electrolyte solution, giving your baby a little at a time. Your doctor may also suggest half-strength formula and other easy-to-digest foods (bananas, applesauce, or rice) for a few days. Mild cases disappear in two to five days. But if your baby is also having trouble keeping fluids down, he could be at risk for dehydration. Call your doctor if your child shows signs of being parched: A sunken soft spot on his skull, few tears, a dry mouth, infrequent urination, lethargy, and a refusal to eat. --Kourtney Eidam
Originally published in Parents magazine, September 2002. Updated 2009.