Forty percent of U.S. children have seasonal allergies. When a parent has allergies, his or her child will probably have them too.

Most allergies tend to appear in childhood. So, if you have seasonal allergies as an adult, you probably started getting them as a kid.

As children, boys get ore allergies than girls, but as they get older, women usually catch up to men.

Even though we say allergies are seasonal, they can occur year-round. In the spring you can get allergies to grass and pollen, and in the fall you can get allergies to ragweed and molds and spores of different kinds.

Allergies occur when pollen, mold or dust kick your immune system into high gear, triggering a release of histamines, those chemicals that are mostly responsible for the sneezing, the runny nose, the itchy throat, and the watery eyes.

If teenagers weren't properly exposed to their environment as children, their immune system won't be able to recognize as harmless the pollen, dust and mold spores around them every day.

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Your immune system is essentially a system of specialized cells and organs that protects you from outside threats such as viruses, bacteria and other biological outsiders.

It is during the first decade of life that it learns which biological intrustions it needs to protect you against.

What this means is, if you don't get exposed to many of the harmless biological threats in your environment during your first decade of life, if you do not challenge the immune system early, you may pay the price with seasonal allergies and asthma throughout the rest of your life.

I'm talking about the dangers of over protecting our children. Some of this overprotection has been institutionalized in the form of widespread use of antibiotics, vaccinations against various diseases, cleaner food and water, and better living conditions.

But some parents may make this "problem" worse by keeping their kids at home in a "sterilized" environment: never taking them to the park, never letting them play in a sandbox, never letting them roll around in the grass, never letting them have a pet at home, and keeping them away from other kids who may be sick.

By underexposing our children to bacteria, certain viruses, and other minor threats in the environment, their immune systems will not develop the appropriate responses, and they may end up with seasonal allergies and other problems of an inexperienced immune system.

Studies show that if you have a pet when you're a kid, you are less likely to get asthma. The same applies to running and rolling around in the grass at the park when you are three years old; those who do tend to have fewer seasonal allergies later on. A little exposure is a good thing.

Allergy Prevention

Prevention is the best treatment for seasonal allergies. Have you heard of spring cleaning? They don't call it that for nothing.

If people in your household have allergies, it is important to do a thorough cleaning of the house, especially in the spring, by removing all the dust that has collected in your house over the winter.

It's a good time to shampoo your rugs, vacuum all the nooks and crannies, and remove the mold from all kitchen, bathroom and garage surfaces.

If you have allergies in the spring and summer, take a few precautionary steps to avoid bringing allergens back into the house.

When you come in from the outdoors, don't bring the clothes you've worn outdoors into the bedroom; change in another part of the house and take a shower, if you can.

Avoid being outdoors from the late morning to early afternoon, as those are the peak hours for pollen production. Keep your windows closed if you're really allergic.

Click here to check out Dr. Manny's book The Check List (Harper Collins, 2007).

Dr. Manny Alvarez is the managing editor of health news at FOXNews.com, and is a regular medical contributor on the FOX News Channel. He is chairman of the Department of Obstetrics and Gynecology and Reproductive Science at Hackensack University Medical Center in New Jersey. Additionally, Alvarez is Adjunct Professor of Obstetrics and Gynecology at New York University School of Medicine in New York City.

Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. Click here for more information on Dr. Manny's work with Hackensack University Medical Center. Visit AskDrManny.com for more.