Pinworms are extremely common. For example, in the United States it is estimated that up to 42 million people have this parasite in their intestines. A common childhood malady, pinworms don't indicate poor hygiene. They pose no health risks, and -- unlike lice -- they are easily eradicated.

People become infected by swallowing or inhaling the eggs. The eggs reach the intestines where they hatch. It takes between two weeks and two months before the female becomes about 1/2 inch in size and mature enough to lay eggs. To lay her eggs, the pinworm migrates from the where the large intestine begins down to the anus. It deposits the eggs by making jerking motions. The current thought is that these motions are what cause the itching. The child scratches his bottom, and the eggs which are quite sticky are picked up and transmitted back to himself or someone else.

Nighttime itching is the big tip-off. You can check for the presence of worms by pressing a piece of transparent tape to your child's anus. Eggs will stick to the tape, and you can take it to your pediatrician to use in making the diagnosis. The doctor may also have a special kit to collect pinworm eggs (the eggs can often be seen even if you can't detect the actual worms).

If you don't find pinworms or eggs, anal itching may signal other problems, including dryness from cleaning the area with a lot of soap. A child who has tender red skin around his anus could also have a bacterial infection; if you suspect an infection, call your pediatrician.

Your pediatrician will prescribe medication -- most often mebendazole -- to kill the worms. (The side effects of mebendazole include diarrhea and abdominal cramping.)

Gaining control over this infection may be difficult due to a number of reasons, so here are some suggestions:

1. Because pinworms are so common and easily transmitted, it is more the rule than the exception that multiple family members are infected even though they may not be experiencing symptoms. Therefore, treatment of the entire family with medication is often required.

2. The eggs are spread from hand to mouth. The eggs have to get to the hands to do this, so limiting access to the anal area can be helpful. This might be done by dressing small children in closed garments such as all-in-one pajamas. Keeping the fingernails short and frequent hand washing will help as well.

3. The eggs will stick to other things in the environment. Simple washing and vacuuming is all that is required. There is no need to go crazy and do an extensive house cleaning, however, concentration on those things the child is regularly touching is more helpful. These items include the bedding, stuffed animals or blankets that occupy the bed, bathroom cups, toothbrush, toothpaste tubes, and doorknobs are some examples.

After treatment, you may see a lot of worms, some moving and wriggling, in your child's stool. Though unsettling, this is no cause for alarm.