This is an irritation or infection of conjunctiva and is sometimes called “pink eye.” There are many causes for conjunctivitis, but these usually fall into three categories: allergic, bacterial, and viral infection. With allergic conjunctivitis, the eye is typically irritated and “itchy.” The eyelids can become puffy, and fluid can collect under the conjunctival skin and bulge it outwards (which looks quite scary). Viral conjunctivitis is what we usually think of as “pink eye.” This is a viral infection of the eye similar to the common cold. Just like a cold, there is no effective treatment other than symptomatic relief and careful hygiene (as viral infections are quite contagious). Bacterial conjunctivitis usually affects only one eye and is associated with purulent (gunk or pus) discharge. This is treated with antibiotic drops. It is often hard (even for the eye doctor) to determine the exact cause of a conjunctivitis. If your eye is red you should see your eye doctor, especially if there is any change to the vision.