Most babies spit up milk out of their mouths or noses. This is because the sphincter at the top of the stomach is often loose. In otherwise healthy, happy babies who are growing well, the spit-up is mostly milk, rather than stomach acid, and nothing needs to be done. (Except a lot of laundry.)

Babies gaining at least 6 ounces a week and with wet diapers at least every 6 hours are usually growing well. On average, spitting up peaks at 4 months and is over by about 7 months of age, though it can take longer.

Spitting up is not likely to be a formula intolerance or allergy to something in a nursing mother's diet. The sphincter at the top of the stomach may be too loose (so it can't hold things in), the valve at the bottom of the stomach may be too tight (so the stomach gets too full), or big air bubbles may take up too much room. Sometimes babies just drink too much, too fast.

Some babies do reflux enough acid that the lining of the esophagus becomes tender, red, and swollen. They might arch their backs in pain. The acid can be inhaled into the lungs, irritating the sensitive linings. These children might not gain weight well, or might cry a lot from discomfort. Some might develop a chronic cough, wheezing, or recurrent pneumonia. A few even stop breathing (apnea) to try to protect their lungs. All of these children need relief from their reflux.

To reduce spitting up, burp your baby several times during and after feeding. Sit the baby upright, with your hand supporting the head. Let the baby lean over slightly, bending at the waist. The upright posture moves air to the top of the stomach, and the forward lean puts a little pressure on the stomach to eject the air, helping the baby to burp. Avoid pressure on the abdomen, which occurs when holding your baby over your shoulder -- this just causes more expulsion of stomach contents.

Here are other ways to reduce spitting up:

• For breastfed babies, try limiting nursing to just one breast per feeding.
• For bottle-fed babies, avoid feeding large amounts. Instead, feed smaller amounts more frequently. Be sure the nipple doesn't have too large a hole.
• Try holding the baby upright for 15 - 30 minutes after feedings.
• Avoid excessive movement and jiggling during and immediately after feeding.
• When it's time to lay your baby down, try keeping the head of his bed slightly elevated.
• Sometimes, switching formulas or removing a food from the mother's diet (usually cow's milk) will help.

If "projectile" spit-up shoots across the room, it's important to consider a condition called pyloric stenosis. Here, the too-tight valve at the bottom of the stomach needs to be treated.