Sneezing, red, swollen, itchy eyes, nasal congestion, wheezing, hives and rashes are signs you may be dealing with allergies. Allergies to grass, weeds, tree pollen and molds may come and go with the seasons.

Cat and dog dander are another common cause of allergies. Food allergies to peanuts or milk can cause cramps, vomiting and diarrhea. Anaphylaxis is an allergic reaction with hives and itching all over, wheezing or shortness of breath, hoarseness or tightness in the throat and tingling in the hands, feet, lips or scalp. Anaphylactic reactions are life threatening and require immediate medical help.

Allergies happen when the body reacts to a foreign substance, or allergen. Once exposed to an allergen, the body begins to produce specific antibodies against it. These antibodies activate mast cells, which are located throughout the body with some higher concentrations in the airways, intestines, skin and elsewhere. These cells release histamine (along with some other chemicals), which causes most of the symptoms of an allergic reaction.