If the suspect saw the baby fussy after drinking milk or certain foods, then there is one way that can help you determine if your baby has an allergy or intolerance. By looking at how fast the reaction occurs.

Allergies
Allergy symptoms usually appear within minutes or seconds. Allergies occur when the immune system a bit chaotic because it reacts with the allergen (substance allergens) in foods and develop antibodies to attack the allergens.
Body to release defensive chemicals, which cause allergic reactions, such as sneezing, swelling or rash, vomiting, and diarrhea. Ask your doctor to diagnose an allergy if you suspect your baby is allergic to.

Intolerance
Intolerance allergy symptoms may be similar, but can not related to the immune system. The main complaint is stomach was churning.

What can be done?
Make a diary of the foods given to infants. This can help you detect that trigger food allergies. Try to only give a new food every four days during the introduction of additional food ASI. This also will help you detect the existence of a new allergic reaction.

Intolerance may be more difficult to diagnose. Both in the case of allergy or intolerance, you should contact your doctor, who will help diagnose the problem and suggest appropriate ways of handling.