What is conjunctivitis? Conjunctivitis is an infection or inflammation of the conjunctiva, the thin membrane that lines the eyelid and also covers the white part of the eye, called the sclera. The delicate tissues of the conjunctiva are protected by the eyelids and the tears, which help wash away irritants and contain infection-fighting antibodies. Sometimes, bacteria, allergens, and other offending substances overcome these protective mechanisms and lead to conjunctivitis. Depending on the cause, conjunctivitis may affect one or both eyes. Conjunctivitis has many different causes, including infections, allergic reactions, and irritation caused by contact with chemicals, foreign bodies, or even misdirected eyelashes. Infectious conjunctivitis may be caused by bacteria, fungi or viruses. One common, highly contagious form of conjunctivitis, often called pinkeye, is caused by a virus. Use of extended-wear contact lenses or improper lens cleaning and storage can also cause an infection. Babies born to mothers infected with Chlamydia or gonorrhea can acquire a serious conjunctival infection during their passage through the birth canal; thus, most hospitals in the United States require that all newborn babies receive preventive antibiotic eye drops. Allergies are another common cause of conjunctivitis. Allergic conjunctivitis may be seasonal, appearing only at certain times of year in response to pollen, or it may be perennial, occurring year-round in response to allergens, such as animal dander or feathers. Physical irritants, such as chemicals and foreign bodies in the eye, can cause conjunctivitis. Abnormalities in the structure of the eyelids can also cause conjunctivitis: if the eyelid turns outward, the conjunctiva is exposed to irritation, and if the eyelid turns inward, the eyelashes can rub on the conjunctiva. Symptoms of conjunctivitis include reddening of the sclera and inside of the eyelids, itchiness, and a gritty feeling. You may have tearing or discharge from your eye, and your eyelids may be crusted when you wake up in the morning. You may have pain and increased sensitivity to light. These symptoms usually resolve with treatment within a few days. Because any eye infection can potentially cause vision problems, contact your health care provider if you have symptoms. Symptoms of blurred vision, sensitivity to light, or double vision following a traumatic injury can be indicative of a serious condition. Extreme light sensitivity and headache can also be a sign of meningitis, a life-threatening condition. Seek immediate medical care (call 911) for serious symptoms if they follow a head injury, such as blurred vision, double vision, light sensitivity, or discharge from the eyes. Any eye infection has the potential to affect your vision. Seek prompt medical care for the symptoms of conjunctivitis.