The inner surface of the eyelid consists of a thin membrane called the conjunctiva. It is one of the places tears are produced, though not to the same extent as in the tear ducts; these tears serve as a lubricant to reduce friction between the eye and eyelid. This layer also helps protect the eye from dust and microorganisms. Despite its usefulness, the conjunctiva is almost never noticed by people until an infection or an allergic reaction causes the inflammation that results in the redness, itching, burning, and sensitivity to light characteristic of conjunctivitis, or pinkeye.
Conjunctivitis can be caused by a viral or bacterial infection, chemical exposure, irritants such as sand or stray eyelashes, or an allergic reaction. Rubbing the eyes makes any form of pinkeye worse, but especially when a chemical or other irritant, or an allergy, is the cause. Bacterial conjunctivitis is possibly the most recognizable form, causing a greenish-yellow discharge that is responsible for a "stuck shut" feeling. Sometimes, pinkeye due to bacterial infection can be associated with a sexually transmitted disease, although this accounts for a very small percentage of eye infections. Bacterial conjunctivitis, left untreated, can cause long-term damage to eye health.
Both the bacterial and viral forms of pinkeye are highly contagious. Someone who has pinkeye should be aware of that and try to take precautions to avoid infecting others, if only out of courtesy. For everyone else, prevention an play a big role in avoiding the disease. Rubbing the eyes can cause or worsen any eye irritation already present, whatever the cause, as well as bringing any microbes on the hands into contact with the eye. Regular hand-washing, such as after cooking using the restroom, or coming in from outside—particularly after using public transit—can also make a significant difference.
Once someone has pinkeye, it is likely to go away on its own faster than most treatments are likely to be effective, particularly it there is no bacterial infection. However, people who have or who have recently had a bout of pinkeye should not wear contact lenses until it is completely cleared up. Eye drops can provide some relief and mitigate irritation.