How do you tell if your baby is allergic or intolerant to something?

Usually, you will not see a quick, visible response to a formula or food. Instead, you might see eczema or another skin rash, fussiness, loose stools, hard stools, or blood in the stool.

In the case of celiac disease, which is an intolerance to the grain protein gluten—not a true allergy—you might see diarrhea, smelly stools, irritability, and poor weight gain.

Allergy testing can be done in babies. At this age, a negative result doesn’t tell you much either way, but a positive result likely indicates a real allergy (as opposed to tests done at age four, when a negative result is likely real, and a positive result may only indicate a possible culprit). There is also specific testing for celiac disease.

If you think your baby may have an allergy, consult your health care provider.