Eye redness may be due to swollen or dilated blood vessels, which cause the surface of the eye to look red. This happens when the vessels in the surface of the white portion of the eye (sclera) become enlarged and irritated. This may result from extremely dry air, sun exposure, dust, foreign body, an allergic reaction, infection, trauma, or other conditions.
Eye infections are conditions caused by microbiological agents such as viruses and bacteria that may cause your eyes to become red and swollen. Conjunctivitis (pink eye) is the most common eye infection. It is an inflammation of the conjunctiva and the inner surface of the eyelids, usually due to a viral or bacterial infection. Sometimes, it can also be due to underlying allergic condition.
The other common kind of redness may be due to subconjunctival haemorrhage, or ‘bloodshot eyes’. This is due to a broken vessel in the eye, which appears very red over the underlying white portion of the eye (sclera). Bloodshot eyes may be accompanied by discomfort or tearing but is usually painless. It may be due to trauma or can occur spontaneously when the fine capillaries of the eye burst from sneezing, straining, vomiting or heavy lifting.
They usually will heal without treatment after a few days to one week. You should consult a doctor should your red eye be associated with pain, blurring of vision, persistent un-resolving red eye or trauma.