The word "allergy" did not exist in Shakespeare's time or even a hundred years ago. It's a modern term for a modern illnessor, more accurately, an assortment of illnesses. Allergy is a catchall word for a variety of reactions made by the body when it detects something foreign. The offending substances may be foods, animal dander, house dust, pollens, mold, smoke, air pollution, medicines or chemicals. The ability of the immune system to identify individual substances and react to them is crucial, but overreaction creates uncomfortable symptoms such as sneezing, sinus congestion, itching or watery eyes, headaches, indigestion, skin rashes, hives and other symptoms.
At any time of year, it can be hard to tell the difference between allergies and cold symptoms. Either can produce sneezes, a runny nose, nasal congestion, an itchy throat and irritated cough. If a "cold" lasts for several weeks, and if your symptoms seem more severe in certain locations (less intense outdoors in winter, for example, and worse in certain rooms or buildings), it's probably hay fever.
According to allergy researchers, indoor or year-round allergies are almost always due to three sources of irritation: the droppings of microscopic dust mites that live in house dust, mold spores and animal dander. In many households, the causes may also include cockroach parts, rodent urine or the smoke from a wood-burning stove or fireplace. All of these irritants are associated with asthma as well.
The orthodox treatment of allergies includes the use of decongestants, antihistamines and steroid drugs. Some allergists specialize in desensitization shots, in which small quantities of allergenic substances are injected into the body over a period of time. Desensitization therapy for bee stings and other insect venoms is generally effective, according to Philip S. Norman in his 1980 overview of immunotherapy published in the Journal of Allergy and Clinical Immunology, while scientific studies on the effectiveness of desensitization to pollen, molds, house dust and animal danders are "generally inconclusive or lacking."
The link between diet and allergies is important, and anyone hoping to relieve hay fever symptoms and allergic reactions to dust mites, pet dander and other common irritants will do well to explore food sensitivities.