Most grown ups' immune cells are found inside the digestive tract, but babies' digestive systems are still developing every day. That's why food allergies are more common in infants than other age groups.
Here’s how it works:
A food allergy develops when a baby’s immune system becomes “sensitized” to an allergen or protein in a certain food. This may happen the first time the baby is exposed to the food, but can also come later.
Once sensitized, the baby‘s body makes antibodies—little proteins that “lock” onto foreign invaders—that are ready to react to that food the next time it’s eaten.
These antibodies then trigger immune cells to make histamine, a chemical that causes allergy symptoms—rash, wheezing, diarrhea, etc.
Feeding choices may help lower your baby’s chances of developing a food allergy. That's why experts suggest having your baby drink only breastmilk for at least the first 6 months of life and waiting until they're at least 4 months old to start appropriate solid foods. Introducing common food allergens around 4-6 months is also recommended. The foods that most commonly cause food allergies in the US are milk, wheat, egg, soy, peanut, tree nuts, fish and shellfish.
The most common symptom of food allergy in babies is atopic dermatitis (AD), a type of skin rash or eczema that most often appears on the face, scalp, limbs and knees. The number of infants with AD has gone up 2 to 3 times over the past 30 years, and nearly 1 in 5 infants will develop AD by 6 months of age. While any baby may develop AD, if the baby's parents or siblings have ever had symptoms of allergies such as hay fever, asthma or AD, or if the parents or siblings have diagnosed food allergies, then they may be at increased risk.
Cow’s milk protein allergy
Cow’s milk protein allergy affects as many as 2–7% of babies. Baby formula is the most common culprit, but babies can also react to the cow’s milk protein that Mom has in her diet, which can be passed through to her breastmilk.
If you think your baby may have a food allergy, talk to your pediatrician as soon as possible to see if allergy testing might be a good idea. They will usually suggest a change to a hypoallergenic formula prior to any additional testing.