Actually, lactose intolerance doesn't typically cause constipation, but conversely causes abdominal pain and often loose stools or diarrhea. When this 1-year-old child suddenly developed hard stools, the problem may seem to have been "caused" by the switch from formula to whole milk, but this is probably coincidental.
All told, this often leads to bouts of constipation that can be managed with the addition of more fluids, bite-sized prunes (which can often be "sold" as raisins to young children) and apple prune juice, or even milk of magnesia if necessary.
Lactose intolerance is defined as the inability to digest lactose, a sugar found in milk and milk products. The problem is due to a deficiency in the enzyme lactase, which is produced by cells lining the small intestine.
Lactose intolerance is uncommon in young children and is typically not seen before the age of 2-3 years. It's more common in older children and teens, who may complain of abdominal pain, cramping, gas, bloating and diarrhea after ingesting dairy products. In most cases, lactose intolerance is diagnosed on clinical history alone, and if suspected, is managed by eliminating dairy products to see if the symptoms improve.
In many cases, even children with a lactase deficiency may tolerate some lactose in their diet, such as a scoop of ice cream, or milk on their cereal, but only experience symptoms when they have "too much milk." Fortunately, there are products like lactose free milk, which will provide a child with the necessary vitamin D and calcium, which is so important during childhood.
Dietary supplements should also be used in children who don't drink milk to meet their daily calcium and vitamin D requirements. Lastly, lactose intolerance is different than a milk allergy, which is fairly uncommon and is due to an allergy to the proteins in milk, not the lactose. True milk allergy usually presents itself in early infancy.
(Dr. Sue Hubbard is a nationally known pediatrician and co-host of "The Kid's Doctor" radio show. Submit questions at http://www.kidsdr.com.)