Conjunctivitis, also known as pink eye, is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may occur. The affected eye may have increased tears or be "stuck shut" in the morning. Swelling of the white part of the eye may also occur. Itching is more common in cases due to allergies. Conjunctivitis can affect one or both eyes.The most common infectious causes are viral followed by bacterial. The viral infection may occur along with other symptoms of a common cold. Both viral and bacterial cases are easily spread between people. Allergies to pollen or animal hair are also a common cause. Diagnosis is often based on signs and symptoms. Occasionally, a sample of the discharge is sent for culture.Prevention is partly by handwashing. Treatment depends on the underlying cause. In the majority of viral cases, there is no specific treatment. Most cases due to a bacterial infection also resolve without treatment; however, antibiotics can shorten the illness. People who wear contact lenses and those whose infection is caused by gonorrhea or chlamydia should be treated. Allergic cases can be treated with antihistamines or mast cell inhibitor drops.About 3 to 6 million people get conjunctivitis each year in the United States. In adults, viral causes are more common, while in children, bacterial causes are more common. Typically, people get better in one or two weeks. If visual loss, significant pain, sensitivity to light, signs of herpes, or if symptoms do not improve after a week, further diagnosis and treatment may be required. Conjunctivitis in a newborn, known as neonatal conjunctivitis, may also require specific treatment.