According to the American Academy of Allergy, Asthma & Immunology, as many as one in five Americans has some form of allergy. About 50 percent of these people suffer from hay fever. Allergies rank sixth in the cost on the list of chronic diseases in the United States.

Pollen counts tend to be highest in the morning — especially between 5 a.m. and 10 a.m. The best time to exercise and do other outdoor activities is mid- to late-afternoon when pollen counts tend to dip.

While genes may predispose a child to an allergy, and children with allergies typically have allergic parents, it is the environment that sets it all in motion. Infants and young children exposed to a lot of pollen, for instance, are more likely to get hay fever than those less exposed, even when hereditary is taken into account.

While people once believed that they were allergic to dust, researchers now know it's not the dust itself, but rather the mites that live in it that cause the problem. Between 100 and 500 individual mites live on a single gram of dust.

Children are most prone to food allergies but many disappear before age 3. Only about 8 percent of kids under age 6 show signs of food allergies — only 2 percent to 4 percent have confirmed food allergies. Only 1 percent to 2 percent of adults have confirmed food allergies.

Allergic reactions to pets are not determined by the breed of animal or the length of hair. The real problem is a protein in the skin and saliva of cats and dogs, not the hair.

After you have been stung once, you may become allergic to that insect's venom. Major offenders: bees, wasps, hornets, yellow jackets and fire ants.

As many as one in every 50 people treated with penicillin develops some type of allergic response. Other drugs associated with allergic reactions include neomycin, novocaine and iodine.

It is the tighter construction of recent years which has led to a greater awareness of "sick building syndrome." The typical residence can contain upwards of 200 different contaminants--especially if built after the late 1970's.

A simple skin test — including prick, intradermal and patch — is actually more accurate and less expensive.

However, while a prick test (also known as a scratch or puncture test) has this capability, it would require 30 separate pricks. More than likely you'll probably be tested only for suspected reactions.

Unless you have a food allergy, there is no need to change your diet in any way. Extra vitamins, minerals or nutritional supplements are not necessary because an allergy isn't caused by a nutritional deficiency.

When an allergen is recognized by one of the antibodies of your immune system, a mast cell is activated to release histamine. Histamine's side effects are the symptoms listed above.

Anaphylaxis is a life-threatening condition which occurs when your immune system goes wild against an allergen, resulting in the most intense allergic reaction. The reaction becomes deadly when it stops your ability to breathe or sends your body into shock. It is a rare reaction that is more often the result of an allergy to insect venom, certain antibiotics, some dyes used in medical tests, or peanuts.

If you have had a severe allergic reaction — to either food or insect venom — you should carry an emergency kit with a syringe of adrenaline (epinephrine) at all times. An auto-injector, the Epi-Pen, is available by prescription. It should be used only as a holding action until you get to an emergency room.

Allergy shots are not useful for food or drug allergies. They are effective against only certain types of allergies, namely insect stings, hay fever and other seasonal pollen allergies. Allergy shots are reserved for people who cannot be helped by drugs or can't avoid their allergen.

Children are, unfortunately, more vulnerable. Childhood allergic reactions include food allergies, eczema, sinus infection and asthma.

A child affected by eczema is more likely to develop hay fever and asthma. Eczema is most common in children with a family history of allergies. Also, children allergic to eggs, milk, peanuts, soy, wheat or fish are most likely to have eczema.

While there have been studies showing that breast-feeding did not prevent or delay the onset of allergies in children, there also have been studies showing that breast-feeding did make a difference, particularly when the diet of the mother was changed at the same time. So, while breast-feeding isn't a guaranteed method of preventing allergies, it can't hurt to try.