Pink eye (or conjunctivitis) occurs when the conjunctiva -- the thin, transparent membrane that lines your eyeball and your eyelid -- becomes inflamed for various reasons. Most cases of pink eye run a predictable course, and the inflammation usually clears up in a few days.
Pink eye is a common disease, especially in children. Although pink eye can be highly contagious (known to spread rapidly in schools or daycare settings), it is rarely serious and will not damage your vision if detected and treated promptly.
There are several types of pink eye, including:
Bacterial pink eye usually infects one eye but can infect both eyes and produces a heavy discharge of pus and mucus.
Viral pink eye typically begins in one eye and causes lots of tears and a watery discharge. Within a few days the other eye becomes involved. A swollen lymph node may be felt just in front of the ear or under the jaw bone. This is probably the most contagious form of pink eye.
Allergic pink eye produces tearing, itching, and redness in both eyes, and sometimes an itchy, runny nose.
Ophthalmia neonatorum is a severe form of pink eye in newborn babies that can be caused by a particularly damaging bacteria. It must be treated immediately by a doctor to prevent permanent eye damage or blindness.
Giant papillary conjunctivitis is another form of pink eye. It is not caused by infection and is most frequently associated with the long-term use of contact lenses.
Pink eye is caused by an irritant. It could be a bacterial or viral infection, a chemical exposure, or a reaction to eye drops. Pink eye can also be caused by an allergic reaction to pollen, smoke, or other substances that irritate the eyes. Sometimes pink eye appears after a cold or a sore throat.
Viral pink eye is easily spread from person to person. Virus strains that most frequently cause pink eye include:
Adenovirus, which often causes the common cold
Herpes viruses, which cause chickenpox, shingles, or cold sores
Some sexually transmitted diseases (STD) can cause conjunctivitis. The STD gonorrhea can cause a rare but very worrisome form of bacterial conjunctivitis. It can lead to vision loss if left untreated. Another STD, chlamydia, can cause conjunctivitis in adults and also in newborns when the disease is passed to the child from its mother during delivery.