| An allergy is a hypersensitive reaction to any of a | | | | headaches. Some allergies may cause hives or an |
| number of substances. Allergies occur when the | | | | itchy rash. Severe allergies can cause the blood |
| body's immune system malfunctions, going into | | | | pressure to drop to dangerously low levels, leading to |
| "overdrive" to help protect the body from a substance | | | | anaphylactic shock and death. |
| it sees as foreign. Allergies are very common in the | | | | Hay fever is an acute type of allergy usually caused |
| United States. In fact, more than one-third of all | | | | by airborne pollens. Trees and grasses are the typical |
| Americans suffer from an allergy of one type or | | | | culprits in this condition. Symptoms of hay fever include |
| another. Common symptoms include nasal congestion, | | | | itchy eyes, mouth, and throat; watery eyes; sneezing; |
| coughing, watery eyes, sneezing, fatigue, and | | | | nasal discharge; and headaches. |