People who suffer from allergies of a specific type are usually prone to allergies from various other substances. These substances, called allergens, range from common indoor household substances like dust particles, mold and mildew, pet dander, chemical emissions from cleaning agents, to biological organisms found in carpeting and furnishings. Outdoor allergens can be pollen, dust and smog from pollution and noxious vapors, insect stings. Common foods which cause allergies are milk, fish, eggs and nuts. Although most allergic reactions are not life threatening, some can cause the patient's blood pressure to plummet or a severe inability to breathe and thus can be fatal. Allergies cannot be cured but they can be treated. There are various types of allergies, some of which have been explained below.

Respiratory Allergies: Common symptoms of hay fever include itchy eyes, nose and throat, along with nasal congestions, coughing bouts and sneezing fits. Hay fever can be caused by a number of allergens including a variety of pollens, all spread by the wind, molds, dust, animal dander. Allergies caused by mold can be from spores in the air, especially found in warm climate or in damp environments like bathrooms and basements. These offending agents like pollen, spores, dust mites, irritating fibers from upholstery and carpets are carried by the air which we inhale.

Skin allergies: These can arise from a reaction to foods, pollen, drugs, insect stings, cold, heat, light and even emotional stress. Symptoms include eruption of hives or urticaria, where the skin erupts into red, itchy, swollen welts that can last from a few minutes to a few days. One may also develop Angioedema, in which there is a deeper swelling around the eyes and lips and sometimes in the hands and feet as well.

Food allergies: Commonly found in infants under two, it is sometimes hard to tell the exact substance that sets off the allergic reaction, as the reaction may be delayed, caused by food additives or maybe due to eating habits. Common offenders are cow's milk, egg whites, peanuts, wheat, soybeans, berries, shellfish, corn and beans. Symptoms manifest themselves as stomach cramps, diarrhea, and nausea. There may be vomiting, swelling of the face and tongue, and respiratory congestion, as well as dizziness, sweating, and faintness.

Asthma: An allergy is one of the most common causes for asthma. Asthma can be caused by respiratory viruses, pollen allergies, mold, animal dander and dust. An allergy can cause the irritation, swelling and inflammation of the air passages, which causes asthma.

Drug allergies: If you're allergic to some drug, it's likely to be from antibiotics of the penicillin family. Antibiotics are the cause of most drug allergies, especially those containing sulfa drugs.

Insect sting allergies: Poison found in the stings of bees, wasps, hornets, yellow jackets, and fire ants is a common allergen.