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Is pink eye always contagious?

/ Source: TODAY

Pink eye, the bane of schoolkids and adults alike, is a common — and often misunderstood — condition.

You wake up in the morning with one or both eyes red and swollen. You're teary, sensitive to light and it feels like there's sand in your eye. Should you stay home, or put on sunglasses and head to work or school?

Conjunctivitis, also known as pink eye, is an eye infection which can be caused by viruses, bacteria or an allergic reaction to pet dander, dust mites or pollen. If it's an infection, it's very contagious. So, even if you don't like the idea of taking a sick day or keeping your child home from school, you should avoid spreading it to other people.

And be careful to wash your hands with soap and water so you don't spread it from one eye to the other.

Eye and face makeup, makeup brushes, contact lenses and eyeglasses can also spread pink eye germs. You should never share them anyway, but if you do have conjunctivitis, it's a good idea to clean them thoroughly before using again.

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If it's an allergy causing the redness, it's not contagious unless a secondary bacterial or viral infection develops, according to the Center for Disease Control and Prevention.

Conjunctivitis usually clears up on its own after a few days. But if it gets worse, you should see a doctor.

Knowing what is causing your pink eye is important. NBC medical contributor Dr. Natalie Azar explains the simple way to tell if it's an infection or allergy in the video above.