Pin worms are small (1/4 -1/2 inch long), white worms that look like small pieces of thread that cause itching around the anus (without a rash), especially at night. Pinworms infect only humans, living in their intestines and are easily transmitted to other people. The adult female pinworm travels to the skin around the anus at night and lays her eggs. When your child itches the area, he will get the eggs under his nails. The eggs are then transmitted to another person, who gets the eggs on their hands and then places their hands in their mouth, swallowing the eggs. The eggs hatch in the intestines and mature into adults, who mate, producing females who can then lay eggs and continue to spread the illness.

If you think that your child has pinworms, you take look at his bottom in the middle of the night and look for the adult worms. If you don't see the worms, your doctor might recommend doing a scotch tape test or using a pinworm prep test to look for the eggs. Scotch tape placed with the sticky part against your child's anus will pick up any eggs that can then be seen under a microscope.

Pinworms are easily treated with an oral medication called Vermox, which is taken as a single dose to kill all of the adult pinworms. A second dose is taken in two weeks to kill any newly hatched pinworms. It is important for everyone in the household (except for pregnant or breast feeding women or children under two years old) to also have treatment, since it is possible to have a pinworm infection and not have symptoms and still be able to spread the pinworms to others. It is also important to wash any clothes or bedding to destroy the eggs.

Another common condition in children that can cause rectal itching is perianal streptococcal cellulitis or dermatitis. This is an infection that is most common in children age 6 months to ten years. It causes a sharply circumscribed area of redness around the anus and requires treatment with antibiotics.