An allergy is an unusually strong reaction{{U}} (31) {{/U}}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{{U}} (32) {{/U}}part of their reproductive process.
Other causes include organisms such as dust mites and molds. Chemicals, plants and dead skin particles{{U}} (33) {{/U}}dogs and cats can also cause allergic reactions. {{U}}(34) {{/U}}can insect stings and some foods.
The most common kind of{{U}} (35) {{/U}}reaction is itchy, watery eyes and a blocked or watery nose. Allergies can also{{U}} (36) {{/U}}red, itchy skin. Some reactions can be life-threatening—for example, when breathing passages become{{U}} (37) {{/U}}.
Avoiding{{U}} (38) {{/U}}causes an allergy may not always be easy. Antihistamine drugs{{U}} (39) {{/U}}offer an effective treatment. Another{{U}} (40) {{/U}}used in some cases is called immunotherapy. A patient is{{U}} (41) {{/U}}with small amounts of the allergy-causing substance. The idea is that larger and larger amounts are given over time{{U}} (42) {{/U}}the patient develops a resistance{{U}} (43) {{/U}}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{{U}} (44) {{/U}}. Every year these allergies cause about thirty thousand{{U}} (45) {{/U}}of anaphylaxis, a severe reaction that requires immediate treatment.
It can result{{U}} (46) {{/U}}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{{U}} (47) {{/U}}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{{U}} (48) {{/U}}are allergic. In other words, a person's immune system overreacts and{{U}} (49) {{/U}}an allergic reaction. The{{U}} (50) {{/U}}common reactions include skin rashes, itching, breathing problems and swelling in areas such as the face.