(HealthDay News) -- The sclera, or white area of the eye, appears red when blood vessels swell.

The U.S. National Library of Medicine mentions these possible causes of eye redness:

• Having a subconjunctival hemorrhage, or burst blood vessel, which could be triggered by straining or coughing.
• Having inflammation or infection of the eyelash follicles or membrane that lines the eyelids.
• Having an ulcer on the cornea (often caused by an infection).
• Having an allergy or the common cold.
• Having foreign matter in the eye.
• Having an injury to the eye.
• Having a bleeding disorder.