"Pink eye" is the common name for conjunctivitis, an irritation of the conjunctiva, a membrane that lines the inside of the eyelids and covers the whites of the eyes. The symptoms are redness in the white of the eye or inner eyelid, itching, irritation and excessive tearing. Sometimes conjunctivitis is an allergic reaction to pollen, dust or other foreign material in the eye - such as contact lens solution. If so, the itching and irritation may be severe, the eyes may be very watery and even painful. Sometimes ordinary household chemicals and personal-care items such as spray perfumes and deodorants cause the irritation. If a chemical gets into the eye, flush the eye with water and call your doctor. If a child gets a chemical into his or her eye, follow the medical advice given on the product, go to the nearest hospital emergency room and be sure to tell the doctors what the substance was.
Conjunctivitis can also be due to a bacterial infection. When it is, both eyes usually are affected, and you may notice a thick yellow discharge crusting over the eyelashes, especially when you wake up in the morning.
Finally, conjunctivitis can be caused by viruses, particularly those associated with colds as well as measles and other childhood illnesses. Viral conjunctivitis is very common. Onset is abrupt and usually in one eye, with the other eye becoming infected a day or two later. Excessive tearing and redness without pus-filled discharge are the usual symptoms.
Bacterial conjunctivitis usually is treated with antibiotic eye drops or ointment but is contagious as long as there is discharge from the eye. Viral conjunctivitis usually clears up on its own within a week and is contagious while symptoms last. To avoid spreading the infections, don't share towels, cups or drinking glasses; wash your hands after applying eye drops or ointment to your eyes (or your child's eye); and don't use eye drops in a non-infected eye that were used in an infected one. Also, don't send children with viral or bacterial conjunctivitis back to school or day care until they are no longer contagious.
Andrew Weil, M.D.