Ever wondered about pinkeye?

One of the most common phone calls I get is from a parent whose son or daughter woke up with pinkeye.

In most cases, the whites of the eyes have turned slightly pink (hence the name), but in some cases, the eyes are very red and the eyelashes are crusted with yellowish goo, or pus.

If lots of goo built up during the night, a child might not be able to open his eyes until he holds a warm, moist compress to his eyelids for a few minutes.

You can't see most of the eye because it's inside the eye socket. The parts you can see include the sclera (the white part), the iris (the colored part) and the pupil (the black part).

One of the most important parts of your eye is the cornea, the part that covers the iris and pupil. It's hard to see the cornea because it's clear. If you look at someone's eye from the side, you'll be able to see the cornea's dome shape more easily.

The sclera is an extremely tough tissue that gives the eye its outer strength. A thin membrane called the conjunctiva covers the sclera and the insides of your eyelids. Under normal circumstances, you can't see the conjunctiva because it's transparent.

The pink or red color of pinkeye is created by blood vessels in the conjunctiva that become enlarged due to inflammation or infection. The medical word for pinkeye is conjunctivitis.

When the conjunctiva gets irritated, the eye becomes itchy or painful.

Here are the most common causes of conjunctivitis:

• Chemical irritation from chlorine in swimming pools, smoke from campfires or barbecues, etc.

• Infections, from either viruses or bacteria.

• Allergies.

• Irritation from rubbing because something got in your eye, such as a speck of dirt or a tiny insect.

Although conjunctivitis is rarely serious, the word strikes fear into the hearts of most parents. Why? Many people assume it's due to infection, and conjunctivitis caused by infection is very contagious.

Because it can be contagious, two things usually happen when conjunctivitis strikes. First, kids with symptoms can't go to school unless a doctor says it's OK or they have been on antibiotic drops for 24 hours. Second, parents might miss work because no one else wants to watch their (possibly) germy kids.

Nowadays, doctors avoid prescribing antibiotics, which treat bacterial infections, unless they're sure you have one. That's why you get a throat culture before someone treats you for strep throat.

The problem with conjunctivitis is that it's difficult to culture someone's eye to see if the redness is from a bacterial infection.

But because conjunctivitis creates so much disruption in people's lives, doctors often treat it with antibiotic drops, “just in case it's bacterial,” so kids can get back to school and parents can get back to work.

Most of the time, that is a reasonable way to go. However, if a child has allergies or has been in a swimming pool recently, you might want to consider treating the child with allergy medicine or artificial tears before calling the doctor.

• Bennett is a Washington pediatrician and the author of “Waking Up Dry: A Guide to Help Children Overcome Bedwetting.”