ABOUT ALLERGIES: Every year, when spring rolls around, millions of Americans start sneezing and coughing. The culprit is allergies. An allergy is simply a negative reaction to a substance that enters the body that is not toxic in itself, yet for some reason causes a bad reaction in the body. Just about anything can be an allergen: dust mites, pollen, cats, dogs, wasps or bees, milk, eggs, peanuts, and even fruits are the most common. A normal immune system is the body's defense against invading bacteria and viruses. It senses potential invaders and attacks them by producing antibodies. But sometimes a person's immune system mistakes a common allergen as harmful. So it produces antibodies to attack them, and this triggers other cells to release chemicals called histamines, causing allergic symptoms.