Food Allergies.
I am a food allergiest, some of the things I see to know the patient has an allergy is: hives, rash, sore throat, puffy in places, etc.
Some ways I treat these are: antihstamine, nasal sprays, or "epipens" in emergencys.
How an allergy occurs is that when you are exposed to an allergen, the body makes antibodies against it. The body readies itself to fight the effects of the substance. the next time it comes in contact with the substance, the antibodies react, causing the realse of histamine from cell tissues. This a the biggest way of causing symptoms. Histamine is in animal and vegetabal tissues, it is harmeless.