Stephanie Lamers, age 13, of Champaign, Ill, for her question:

WHAT CAUSES CONJUNCTIVITIS?

Conjunctivitis is any inflammation of the membrane covering the outer layer of the eyeball and the inner lining of the eylids. This membrane is called the conjunctiva. In conjunctivitis, the eyes become red and watery and sometimes pus may form.

Acute conjunctivitis, which is also called pinkeye, is caused by bacteria and viruses that can be spread to others by using the same towel. Doctors cure bacterial conjunctivitis with antibiotics or sulfanamides.

Viruses that can infect the conjunctiva include those that cause colds and measles.

Other viruses sometimes infect the conjunctiva and cornea, which is the clear tissue over the colored part of the eye. Victims may lose part or ail of their sight.

The conjunctiva can also become inflammed by smoke, certain eye drugs and substances that cause such allergies as hay fever.

Symptoms of acute conjunctivitis may sometimes last four years and result in a relatively rare contagious eye disease called trachoma. Trachoma affects the conjunctiva and also the cornea, the window of the eyes.