There are several blood vessels located on the different surfaces of the eyes. Red eyes or bloodshot eyes occur when these vessels become dilated or irritated, causing a reddish appearance to the eyes. This expansion of the blood vessels, known as vasodilation, makes the whitish portion of the eye (the sclera) appear red. In some cases, the irritation may cause individual blood vessels to become more visible. In more severe situations, these blood vessels can rupture, causing blood to leak into the eye, resulting in noticeable redness or a subconjunctival haemorrhage.

This fact sheet is part of our Ophthalmology and Optometry Information Guide series, developed to help people understand eye conditions and their impact on navigating the built environment.