What do you think of when you hear the words "camping trip"? Close your eyes and try to imagine the taste of food cooked over a campfire, and the fun of scrambling up a rocky trail to see a beautiful view. Think about how nice it feels to fall asleep snuggled in a sleeping bag as a cool breeze blows through your tent flap.

Wait a minute. What's that whining, buzzing noise? Oh, no. It's a mosquito, and it's dive-bombing your head. You struggle out of your tent, and stumble into a patch of leaves. You point your flashlight down at them to see where you are -- and you notice they have three shiny leaves. Poison ivy! Yes, camping out is fun. But there can be some annoying -- and itchy -- parts to it, too.

Your skin protects your body pretty well most of the time. But there are some things it isn't equipped to handle without swelling up and itching. One of these is the bite of a female mosquito. Almost everybody is allergic to mosquito bites. When the insect bites you -- and only females do -- it drinks a tiny drop of your blood. In exchange, it leaves behind a small amount of saliva.

Certain things out in the world -- mosquito saliva, poison ivy, poison oak and other materials -- contain chemicals which cause allergic reactions in human beings. Chemicals which trigger these reactions are called antigens. When antigens touch the skin, special chemicals called antibodies rush to the site to fight them. When antibodies react with antigens, they cause special cells in the skin to release histamine.

Histamines cause fluid to leak out of your blood vessels into your tissues, making your skin swell up.The skin's sensitive nerve endings are disturbed, and you itch. Try not to scratch the bumps caused by mosquito bites, though. That only makes the reaction worse.

"Leaves three, let them be," goes the old saying about poison ivy. That's good advice. But it can be hard to avoid the three-leaved plant. It's extremely common in the Washington area. You may see it along bike paths, hanging from trees in the park, or even growing in your back yard. It's a good idea to learn to recognize and avoid poison ivy.

If you do get into it by mistake, rush to the sink and wash the area where the plant touched you with lots of soap and water. You may be able to head off the reaction. It's more likely, however, that you'll see the rash appear. It may show up in a few hours, or it may not appear for a few days.

Poison ivy and its relatives, poison oak and poison sumac, contain an oil which sticks to anything that brushes against them. Your bike tires, your dog's coat, or your shoes can pick up the oil. Then you may get poison ivy even if you didn't touch a single plant directly. It's a rare person who doesn't ever get the little white, itchy bumps these poisonous plants cause. Nearly three-quarters of the American population is allergic to the plant.

Once the itchy poison ivy bumps appear, you probably start wondering how long you are going to have to suffer. "That differs from person to person," says Dr. Henry Palacios, an allergy specialist in McLean, Va. "Some people are much more sensitive than others. Some cases of poison ivy clear up in a few days. Others last longer."

At the drug store, your parents can ask the pharmacist about creams containing allergy-fighting substances called steroids. These creams are very effective against poison ivy, any itching of mosquito and other insect bites. If you put steroid cream on your poison ivy or bites, they should feel better right away -- and start to disappear after a couple of days.

Some people are so sensitive to poison ivy that they experience very severe reactions to it. They swell up, and may become feverish and sick. When that happens, it's a good idea to see a doctor who can give you a medicine by mouth or shot to stop the allergic reaction. It's also a good idea to see a doctor if you have large areas of poison ivy rash on your skin.

But a minor case of poison ivy can be treated with things you probably have in your kitchen cupboard. To soothe the itch, apply a paste of baking soda and water, or soak in a tub of cool water with a couple of cups of cornstarch added to it.

Calamine lotion, another remedy available at the drugstore, also helps. It's also effective on itchy mosquito bites. If you had been on our imaginary camping trip described earlier in this story, you'd probably be dotted with the pink calamine lotion by now. Tips for Parents

Have your children color the leaves on this drawing of poison ivy a shiny green. They can use a red crayon on the stems since, during the summer, the stems are reddish green and in the fall the whole plants takes on a bright reddish tone. You might cut the picture out, and tape it to your refrigerator. When it comes to poison ivy, it's a good idea to know your enemy.