A baby may drink a normal amount of milk but have increased loss of fluid, due to diarrhea, and become dehydrated. More frequent feedings can help prevent dehydration, but keep an eye, in conjunction with your physician, on the baby. Babies can also lose fluid from vomiting. It is usually more forceful in nature and larger in volume. Spitting up often occurs right after a feeding, while vomiting can occur at any time.
Vomiting can cause dehydration or be a sign of serious dehydration.
Vomiting may be the result of dehydration, intestinal blockage, or infection. A common sign of infection is fever. The best way to take your baby's temperature is with a rectal thermometer placed in the rectum. Using thermometer strips on the forehead and touching to determine temperature are not reliable ways to learn of a fever. In babies less than 3 months of age, a temperature greater than 100.5 may be a sign of a potentially serious infection, so you should call your doctor immediately.