Conjunctivitis is an inflammation or infection of the membrane lining the eyelids (conjunctiva).

The conjunctiva is exposed to bacteria and other irritants. Tears help protect the conjunctiva by washing away bacteria. Tears also contain enzymes and antibodies that kill bacteria.

There are many causes of conjunctivitis. Viruses are the most common cause. Other causes include bacteria, Chlamydia, fungi, and rarely, parasites.

"Pink eye" refers to a viral infection of the conjunctiva. These infections are especially contagious among children.

Bacteria are an uncommon cause of conjunctivitis. Conjunctivitis is also caused by allergies (allergic conjunctivitis), chemical exposure, and certain systemic (throughout the body) diseases.

Newborns can be infected by bacteria in the birth canal. This condition is called ophthalmia neonatorum, and it must be treated immediately to preserve eyesight. Use of contact lenses, particularly extended-wear lenses, can cause conjunctivitis.

See also:

• Allergic conjunctivitis
• Keratoconjunctivitis sicca
• Neonatal conjunctivitis
• Trachoma
• Vernal conjunctivitis

• Blurred vision
• Crusts that form on the eyelid overnight
• Eye pain
• Gritty feeling in the eyes
• Increased tearing
• Itching of the eye
• Redness in the eyes
• Sensitivity to light

• Examination of the eyes
• Swab of conjunctiva for analysis