This is the VOA Special English Health Report.

An allergy is an unusually strong reaction to a substance. Many things can cause allergies. The most common cause is pollen. Trees usually produce pollen in the spring, grasses in the summer and weeds in the fall as part of their reproductive process.

Other causes include organisms such as dust mites and molds. Chemicals, plants and dead skin particles from dogs and cats can also cause allergic reactions. So can insect stings and some foods.

The most common kind of allergic reaction is itchy, watery eyes and a blocked or watery nose. Allergies can also cause red, itchy skin. Some reactions can be life-threatening -- for example, when breathing passages become blocked.

Avoiding whatever causes an allergy may not always be easy. Antihistamine drugs may offer an effective treatment. Another treatment used in some cases is called immunotherapy. A patient is injected with small amounts of the allergy-causing substance. The idea is that larger and larger amounts are given over time until the patient develops a resistance to the allergen.

In the United States, experts estimate that up to four percent of adults and up to eight percent of young children have food allergies. Every year these allergies cause about thirty thousand cases of anaphylaxis, a severe reaction that requires immediate treatment.

It can result in trouble breathing and in some cases death. The National Institute of Allergy and Infectious Diseases says one hundred to two hundred people die. It says most of the reactions are caused by peanuts and tree nuts such as walnuts.

People can also be allergic to medicines. The American Academy of Allergy, Asthma and Immunology says about five to ten percent of bad reactions to commonly used medicines are allergic. In other words, a person's immune system overreacts and produces an allergic reaction. The most common reactions include skin rashes, itching, breathing problems and swelling in areas such as the face.

But the academy estimates that allergic reactions to drugs cause one hundred six thousand deaths each year in the United States alone. It says antibiotics such as penicillin are among the drugs more likely than others to produce allergic reactions. So are anticonvulsants and hormones such as insulin. Other kinds include some anesthesia medicines, vaccines and biotechnology-produced proteins.

And that's the VOA Special English Health Report, written by Mario Ritter and Caty Weaver. I'm Steve Ember.