An allergy is an immune system response. We all have an immune system that gets rid of unwanted bacteria and viruses that make us sick. A food allergy occurs when the immune system mistakenly reacts to a food protein. The food protein causing the problem is called an allergen.

Cow's milk protein allergy occurs when your baby's immune system reacts to the proteins found in cow's milk and treats those proteins as allergens. The result is an allergic reaction. The symptoms can include diarrhea, blood and/or mucus in the stools, red itchy scaly skin, vomiting, congestion, wheezing, running nose and hives.

If your baby is allergic to cow's milk, it is possible she will also be allergic to milk from other animals, such as goat's milk. Soy formula may also cause a reaction. It's best to check with your baby's doctor before trying these other formulas.

Although it is not known why any particular baby will be allergic to cow's milk protein, there are at least three things that make it possible: 1) your baby's immune system is still very immature, meaning it is less able to distinguish harmful foreign substances from harmless protein; 2) the whole proteins in cow's milk are made up of long strings of amino acids, which are able to stimulate an allergic response; and 3) your baby may have a stomach and intestine which are very sensitive to allergens. If the protein causes an immune system response, it causes allergic symptoms. What's worse, if the problem goes on long enough, your baby may not gain weight and grow like he should.

The most popular routine infant formulas contain whole (intact) proteins, similar to breast milk. Formulas designed for mild intolerances, such as fussiness or gas, have the proteins partially broken down. These formulas are known as partially hydrolyzed and are not appropriate for babies with food protein allergies. There are also specialized formulas for infants with allergy symptoms who need an extensively hydrolyzed formula (the protein chains are broken down even further).

Soy protein allergy is similar to cow's milk allergy, but it is the soy protein that causes an immune system reaction.

Multiple food protein allergies are a reaction by the body's immune system to the protein in two or more foods. When the food is eaten, a chain of chemical reactions occur within the body, causing symptoms such as itchy skin, hives, diarrhea, vomiting, and, sometimes, difficulty breathing. Most allergic reactions occur within 30 minutes of eating the food, but can occur as much as 4–6 hours later.

In young children, the foods most likely to cause allergies are cow's milk , eggs, wheat, and peanuts.

A food intolerance does not involve the immune system. Lactose intolerance is the most common type of food intolerance. Symptoms can include gas, bloating, stomach pain, or diarrhea. However, lactose intolerance is rare in babies and young children.

Although the incidence of cow's milk protein allergy is very low in breastfed infants compared to formula-fed infants, it does happen. It is not an allergy to breast milk itself. Instead, the allergy usually begins after proteins, including cow's milk protein, are passed from mom to her baby through breast milk. The symptoms may begin right away or it's even possible for some very sensitive breastfed babies to develop a milk allergy from breast milk but not have a reaction until they actually drink cow's milk.

If you are breastfeeding and your baby is showing allergic symptoms, elimination of common allergens such as cow's milk, eggs, fish, peanuts, and tree nuts (eg, almonds, pecans, and Brazil nuts) from your diet could help relieve the symptoms. It's best, though, to check with your doctor or dietitian, to let them guide you on what to eat while breastfeeding.

If this doesn't help the symptoms, check with your baby's doctor.

Even though children of parents with food allergies may develop food allergies, true food allergies are not as common as you might think. According to the American Academy of Pediatrics (AAP), 2% – 3% of infants are allergic to milk. The American Academy of Allergy, Asthma & Immunology reports that up to 8% of infants and toddlers may experience food allergic reactions, and 2% of adults experience food allergies. The common foods causing allergic reactions among adults are peanuts, tree nuts (eg, almonds, pecans, and Brazil nuts), fish, and shellfish.

Most children outgrow cow's milk protein allergy by the age of 3. However, this is not always the case. Doing something about the allergy as early as possible helps. Here are some other things you can do to lower the risk of food allergies for your baby:

• Don't introduce solid foods until at least 6 months of age.
• Breastfeed your baby until at least 1 year of age, if possible.
• Introduce new foods in small portions and one at a time. Watch for a reaction (several days) before introducing the next food.
• Talk to your baby's doctor about delaying foods that commonly cause allergies such as peanuts, egg whites, or fish, until past age 2.

Nutramigen AA LIPIL does not contain whole proteins The protein in Nutramigen AA LIPIL is single amino acids, which are the building blocks of proteins. Because amino acids are smaller than whole protein chains, your baby's body can digest and absorb them without risk of stimulating an allergic reaction. That means your baby can use Nutramigen AA LIPIL for normal growth and development.

Here are some Web sites that will be helpful–

• Food and Nutrition Information Center of the National Agricultural Library/USDA
  Choose Topics A–Z, then highlight Allergies and Food Sensitivities
• http://www.foodallergy.org or phone 1-800-929-4040