A: Bobbie, it sounds like your son may have a milk allergy.

Prosobee is a soy-based (rather than cow's milk-based) formula, which is also lactose-free. Your doctor would have recommended it if your baby had showed signs of milk allergy or milk/lactose intolerance, such as vomiting or diarrhea after feedings. If your son was fine on the Prosobee formula and then vomited shortly after drinking a small amount of skim milk (which has cow's milk protein, the allergy-causing component of milk), this probably indicates that he's still allergic to milk. Signs of food allergies usually appear within 10 minutes to two hours after eating the food. In addition to vomiting or diarrhea, other signs of food allergies include hives, itching, swelling of the tongue and throat, runny nose, wheezing, coughing or difficulty breathing.

Milk allergy is one of the most common food allergies in young children, affecting 3 to 4 percent of infants. To confirm whether your son has a milk allergy (and maybe other allergies as well), your doctor might do a blood test or refer your son to an allergy specialist for skin tests. If your son does have a milk allergy, the doctor can help you plan your son's diet to avoid allergic reactions, and prescribe medications in case of an allergic reaction. In addition, a consultation with a nutritionist can be helpful to plan a nutritious diet and avoid exposure to milk products in foods.

Children can grow and develop well without drinking milk or eating milk products if they drink enriched soymilk and other foods that are high in calcium and protein. You should avoid any type of cow's milk (including skim, dried, solid, evaporated and condensed), cheese, yogurt, ice cream, butter and buttermilk. Also, be sure to read all food labels (including on baked goods, premixed cereals, luncheon meats, margarine and soy products) to avoid the milk proteins casein, caseinate, lactalbumin and whey.

About three out of four infants diagnosed with milk allergy will outgrow it, often by 3 to 6 years of age. It's important that you work closely with your baby's doctor to determine the right time and procedure for trying to reintroduce cow's milk. Rarely, a child can have a severe allergic reaction, and you need to be prepared for that possibility. Your doctor may recommend that you keep your baby away from milk products until he's 12 to 18 months old. Then she may recommend retesting your son every six months until she determines that he's no longer allergic to cow's milk. Don't give your son any more milk or milk products except under the supervision of your doctor.

If your son ever has a severe reaction to milk (with breathing problems and loss of consciousness, known as anaphylaxis), the doctor may recommend that you try milk only under close medical supervision, such as in a hospital.