Conjunctivitis, also known as "pink eye," is a common eye condition. It's an inflammation of the conjunctiva, the membrane that covers the white of the eye and the inside of the eyelids. Within this membrane, there are tiny blood vessels that get enlarged when the conjunctiva become irritated. The enlarged blood vessels make the eye look red.
The most common causes of conjunctivitis are viruses and bacteria, but other causes include allergies, ultraviolet light, and chemical or environmental irritants.
Viral conjunctivitis is caused by the same viruses that are also often responsible for the common cold. These viruses are highly contagious (easily spread from person to person), and anyone can transfer the virus to his or her eye by blowing their nose with their eyes open or rubbing their eyes.
Bacterial conjunctivitis is caused by various types of bacteria. Bacterial conjunctivitis is also contagious and usually requires a short course of antibiotic eye drops or ointment.
Allergic conjunctivitis is not contagious and usually occurs in the spring, summer, and early fall. It is usually triggered by exposure to plant pollen and grasses. People who are allergic to animals or dust mites may be affected year-round.
Chemical or irritative conjunctivitis is also not contagious and is caused by exposure to irritants including:
Conjunctivitis may also occur in people with certain medical conditions. These include thyroid disease, gout, certain types of cancer, tuberculosis, and syphilis.
Signs and symptoms of conjunctivitis include:
Serious complications of conjunctivitis are very rare.