Intolerance vs. allergy: What’s the difference?

Milk protein allergy is the most common food allergy in infants.

But tummy troubles don’t necessarily mean your baby has an allergy; it could be an intolerance (or sensitivity). That’s a common misunderstanding, Dr. Goldman says.

Sensitivity to dairy or soy. This is much more common than an actual allergy to milk and is what Dr. Goldman says she sees most often in her practice. Parents bring in an infant that is irritable and spitting up a lot, and they may see little flecks of blood in the stool.

This is frightening for new parents, but Dr. Goldman says you can easily resolve it by switching to a dairy- or soy-free formula and avoiding dairy and soy yourself, if you are breastfeeding

Soy protein is similar to cow milk protein and often prompts a similar reaction in children who have this sensitivity, she says.

Milk protein allergy. An actual allergic reaction to milk protein is much less common. During an allergic reaction, an infant’s immune system sees milk proteins (casein and whey) as a foreign material. It creates antibodies against the offending proteins, triggering the release of chemicals such as histamine.

With this cycle going on, your baby is likely irritable and may seem inconsolable. Symptoms may include:

Stomach inflammation and cramping
Vomiting or excessive spit ups
Blood in the stool
In severe cases, anaphylaxis, an emergency requiring immediate medical attention and a shot of epinephrine
Symptoms don’t always show up right after birth, since the body may take time to react to the protein exposure. They usually begin in an infant’s first few weeks, though, and may show up even months later, Dr. Goldman says.