What do swimming pools, smoke-filled clubs, and dusty attics have in common? They can all result in bloodshot eyes. Whether its chlorine, smoke, or dust, anything that invades and irritates your eyes can make them appear red and swollen.
"Bloodshot" is precisely the right term to describe what happens when something irritates the eyes. If you look very closely in the mirror, you'll see that the whites of your eyes contain thousands of tiny blood vessels. Normally, the vessels are so small that they don't discolor the eye's white areas. But when a piece of dust or pollen or any other irritant gets in your eyes, the vessels become engorged with blood and the eyes appear red.
Redness is part of the body's normal response to irritation or injury. When an area becomes irritated or inflamed a few things happen. First, extra blood flows to the problem area. Meanwhile, mast cells located in the inflamed area release chemicals such as histamine that aid in the healing process by making the blood vessels more porous. This allows blood plasma proteins and white blood cells to enter the inflamed tissue, where they target the irritant and destroy it.
So, although bloodshot eyes may look gruesome, they're just a sign of the body healing itself. As for the reducing engorged blood vessels, give your eyes a rest and the redness will disappear in time.