Brief Answer:
Conjunctivitis

Detailed Answer:
Hello, I'm Dr. Branch, thanks for using 'Ask a Doctor'. There can be many causes for a red eye, some dangerous, while most of the time it is nothing serious. If you have any vision changes, you are not able to keep the eye open in light, or it feels like there is something in the eye, these would be signs of possibly something serious, and you should see a doctor as soon as possible. Otherwise, the most likely diagnosis is conjunctivitis, or "pink eye". This can be from a bacterial infection, viral infection, or allergies. If you have a lot of discharge coming from the eye, especially throughout the day, it is more likely bacterial and you should see a doctor about getting antibiotic drops. If not, and you have other symptoms like runny nose or cough, it is more likely viral, and you don't need to treat it with anything, though you should be careful to try not to touch the eye and wash your hands frequently, as it is very contagious. If you have sneezing or eye itchiness, this could be allergies, and you could treat with an antihistamine such as Claritin or Zyrtec.

I hope that helps, please let me know if you have any other questions about that, and I would be glad to discuss it with you further.

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