But most gastrointestinal symptoms develop over the course of days and weeks. Of greatest concern are those babies with asthma who may have difficulty breathing due to swelling of the upper airway and may have an anaphylactic reaction. Milder reactions include eczema, hives, and skin rashes. Irritability and excessive crying, which mimic infantile colic are additional symptoms. If milk allergies persist, they may inhibit the baby's growth.
Milk allergies are due to an immunological reaction against proteins called casein or whey.
When allergic babies are exposed to these proteins, which may be considered foreign intruders, they become sensitized, and with each subsequent exposure the symptoms are likely to worsen. Sensitization may even occur during the last trimester of pregnancy via the ingestion of dairy products in the mother's diet, causing symptoms to develop immediately after birth. For babies with milk allergies, a complete dietary change is necessary to avoid all products containing casein or whey. Hypoallergenic formulas are a good substitute since the milk proteins are already broken into pieces which the baby can tolerate. These formulas contain all the vitamins and iron that babies require during the first year of life.