Dr. Greene, our 19-month-old son has seemed to have trouble since his birth. He wouldn't be miserable all the time, just a good portion of the time. At 1 year, he was introduced to cow's milk. Before this time, he had consumed cheese and a few other dairy products. He is a very unsettled, miserable-acting child. As his mother, I know something is wrong. He has been having trouble with constipation for a while now. We have tried increasing fruit, veggies, and whole grains to no avail. He goes for days between stools, and when he does eliminate, there is a very hard, very large "plug" of stool that comes out, followed by two to five diapers full of loose stool within a couple of hours. His father is lactose intolerant yet can drink skim milk with no problems. My question is: should we try skim milk? Or should we try a lactose-free type of milk or soymilk? Any help would be appreciated greatly!!!

A cranky, unhappy toddler may well be responding to physical discomfort. Tummy troubles of one type or another can make anyone feel miserable. Milk is a major part of most children's diets. If a child is intolerant to milk, this can affect how he feels every single day of his life. Nausea, cramps, and pain can squelch the normal joys of discovery and mastery.

But the classic symptoms of milk intolerance are diarrhea, spitting up, or abdominal pain. Many kids with milk intolerance also wheeze, especially when they get a cold. They can also have the dry, sensitive skin of eczema and their noses always seem to be running. Ear infections are also more common than in other kids. Constipation, however, has not been typically associated with milk intolerance -- until now.

The observation that constipation might sometimes be caused by milk intolerance has appeared in the medical literature from time to time, dating back as far as 1954 (Pediatric Clinics of North America, 1954; 4:940-962). But only recently has there been a well-designed study published showing that this is indeed the case. The results of this study, when widely known, can set many children free to enjoy the exuberance of childhood without pain.

Researchers at the University of Palermo in Italy worked with 65 children with chronic constipation. All of these children had been treated with laxatives when dietary measures had failed. Even with the medical treatment, these children were still constipated, having hard, painful stools only every 3 to 15 days. Forty-nine of the their little bottoms had fissures and redness or swelling from the hard plugs of stool.

Each child received either cow's milk or soymilk for 2 weeks, with no one knowing which was which. Next, they had a week during which they could eat and drink anything they wanted to wash out the effects of the first 2 weeks. Then they switched sides for 2 weeks and got the milk that they didn't get the first time. Careful recordings of the bowel habits were made.

When the secret code was broken at the end of the study, they found status quo constipation for each child while he or she was on cow's milk. But while they were taking soymilk (which causes firmer stools in most kids), 68% of these kids were no longer constipated! The redness, swelling, and fissures on their bottoms healed (New England Journal of Medicine, 1998; 339:1100-1104). How wonderful to finally have relief after diet and medicines hadn't worked for so long!

The results were most dramatic in kids who also had frequent runny noses, eczema, or wheezing. Nevertheless, sometimes constipation can be the only symptom of cow's milk intolerance.

This has broad implications. The children in this study were those with severe chronic constipation that was unresponsive to medications. I am convinced that they are only the tip of the iceberg. There must be a much larger group of mildly allergic children whose constipation improves with laxatives. Time may prove that it is better for these children to avoid the offending protein by switching milks rather than being treated with laxatives.

Presumably, swelling of the intestinal lining causes the constipation. Whatever the exact mechanism, the problem is likely with the protein in cow's milk, not with the fat or lactose (the sugar).