Summer is here, and it's time to prepare for a little jungle warfare. Stepping into the great outdoors makes your body fair game for stinging bees, biting insects and, worst of all, the plague of poison ivy.

    Nearly half of Americans are allergic to poison ivy and its 150 plant cousins, reacting with a skin rash known as allergic contact dermatitis.

    You aren't allergic to poison ivy the first time you touch it -- it takes about 10 to 14 days for your body to develop the allergy through a process known as sensitization. Once your body becomes sensitized, repeated exposure leads to a delayed skin reaction and a rash that generally appears in 24 to 72 hours.

    The offending agent in poison ivy is the oil, or oleoresin, found in every part of the plant. The tiniest drop can set off a chain reaction of allergic events, causing skin cells to release corrosive chemicals that produce the characteristic red, oozing blisters.

    Contrary to urban legend, leakage of the blister fluid doesn't spread the rash to other parts of your body, or to other people. Only contact with the oil of the poison ivy plant causes allergic contact dermatitis.

    If you accidentally grab a poison ivy plant and then shake hands with your unsuspecting neighbor, you can contaminate him with poison ivy oil. But if you shake his hand four days and four showers after touching the plant, you won't contaminate him even if your hand looks like it's got a bad case of leprosy.

    The problem with poison ivy is that you usually don't realize you've touched it until it's too late. You may have been exposed through no fault of your own: Your dog may have rolled in the stuff right before he greeted you with a big furry hug.

    Once the poison ivy oil is on your hands, it's easily spread to every surface you touch. You might go about your business for hours, scratching your nose and rubbing your eyes.

    Heaven forbid you should take a potty break and wash your hands afterward, and not before. A microscopic drop of poison ivy oil can produce a mass of itching, crusting blisters on any part of your person.

    By the time you start to itch, it's likely that one to four days have passed since you were contaminated. At this point, it's almost impossible to stop the developing rash.

    If your suffering is especially prolonged or severe, you may seek medical attention. In addition to offering sympathy, some physicians prescribe steroid medications to treat the rash and itching.

    Steroid drugs work by suppressing the immune system and may reduce the severity or duration of symptoms. Depending on your degree of desperation, you can take your steroids by injection or by mouth -- or you may choose to apply them to your ravaged skin in the form of a cream or gel.

    Since steroids are known to stimulate the appetite, you may have to decide if you'd rather be thin and miserable or fat and happy.

    Although a great deal of energy is directed at drying oozing blisters, the skin eruption resolves only when the allergic reaction has stopped. Pink products like calamine lotion help draw sympathy and may alleviate itching, but they really don't get rid of the rash.

    Experienced poison ivy sufferers will tell you that the best way to endure the symptoms is to sleep through them. Taking an over-the-counter antihistamine can alleviate the itch and make you sleepy enough to put you out of your misery for a few hours.

    If you know you've been exposed to poison ivy, make a beeline for the shower, and spend at least 20 minutes decontaminating yourself with plenty of soap and warm water. Don't forget to wash your clothes and douse your tools and shoes with rubbing alcohol to remove the poison ivy oil.

    The best form of poison ivy prevention is recognition, and it behooves anyone with skin to find a photograph of the plant and commit to memory. Poison ivy can disguise itself as a plant, vine or shrub with notched leaflets in groups of three that are bright green in summer and brilliant red in fall.

    Once you know what the plant looks like, you've got a better chance of surviving at least one of the dangers of the great outdoors. Be careful -- it's a jungle out there.

 
    Rallie McAllister is a board-certified family physician, speaker and the author of several books, including "Healthy Lunchbox: The Working Mom's Guide to Keeping You and Your Kids Trim." Her website is www.rallieonhealth.com.