PEDIATRICIAN DR.PAUL Answers: I am glad you asked this question as it brings up the point of exactly how cow's milk allergy differs from lactose intolerance. In order to understand the difference, one must know exactly what makes up cow's milk.

Ordinary cow's milk contains three basic components: protein, sugar - specifically lactose - and vitamins and nutrients such as calcium. When we talk about cow's milk allergy, which is the most common food allergy in children, we mean that a child is actually allergic to the protein in cow's milk. In other words, the body reacts to the cow's milk protein, producing symptoms which can range from rash, difficulty breathing and swelling of the face and mouth area, to excessive crying, vomiting or diarrhea.

Lactose intolerance, on the other hand, is the intestine's inability to digest the milk sugar "lactose". Lactose in milk cannot be readily absorbed by the body. But ordinarily, everyone has an enzyme in their digestive system called lactase which breaks down lactose into smaller parts that the intestine can absorb. In cases of lactose intolerance, the lactase enzyme is either absent or reduced, leaving the person unable to properly break down the lactose and digest it. The lactose then remains in the intestine, causing the typical symptoms of lactose intolerance which include: excess gas, bloating, abdominal pain and diarrhea. Permanent lactose intolerance rarely occurs in children, but as they get older it can develop, and in some ethnic groups, the rate of lactose intolerance in adults is quite high. Temporary or transient lactose intolerance can occur in children often after a bout of gastroenteritis, which causes a temporary decrease in intestinal lactase, but this usually resolves within a few weeks.

Unlike lactose intolerance, cow's milk protein allergy can be very dangerous. A child with cow's milk allergy should not be given any dairy products at all. Babies on formula who have cow's milk allergy are given special formulas containing no cow's milk protein. They are usually soy-based products (Isomil, Prosobee and Nursoy) or hyrdrolysate formulas ( Nutramigen and Alimentum). In this case, switching from one type of regular infant formula to another is not an option because all regular formulas contain cow's milk protein. Additionally, lactose-free cow's milk or formulas should not be given to cow's milk allergic children because they need to completely avoid cow's milk protein. Most children will outgrow their milk allergy within the first two years of life, but your child should have an allergy test before re-starting cow's milk protein containing diets.

Lactose intolerance is not dangerous but can cause discomfort. The treatment is simply to avoid lactose in milk which is easily achieved by using lactose-free cow's milk and taking pills such as Lactaid or Lactease before eating lactose-containing foods. In this situation, cow's milk protein is not a problem and therefore should not be avoided.

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