The Common Health Issue Justin Bieber Wants You To Know About

In case you missed it, Justin Bieber has conjunctivitis in his left eye. Yesterday, Biebs posted a series of five identical selfies of his eyeballs on Instagram, informing his 87 million followers about his condition.

The first two posts say, "My left eye has conjunctivitis." The next one says, "This eye has conjunctivitis." The fourth post reads, "You can see it better here." And finally, the last post simply says, "Conjunctivitis." Conjunctivitis is not a health phenomenon you usually hear celebs bragging about, but it's actually a very common eye infection, according to the American Academy of Ophthalmology (AAO).

Never heard of conjunctivitis? It's also called "pink eye," because when you get it, your eye gets red and swollen, according to the AAO. You can get conjunctivitis in one or both eyes (Bieber has it in his left eye), and it happens when the clear tissue covering the white part of your eye and the inside of your eyelid (a.k.a. the "conjunctiva") becomes irritated because of an allergy or infection.

Aside from becoming red and puffy, your eye might feel painful, watery, or itchy, or like there's something in it. And your vision may get blurry or hazy. Unlike when you scratch your eye, which can cause similar symptoms, when you have conjunctivitis, your eye will produce lots of mucus, pus, or discharge. Fortunately, even though conjunctivitis can be uncomfortable, it's usually not a huge deal.

So, how did Biebs get it? That's hard to say. But, according to the National Institutes of Health (NIH), there are three types of conjunctivitis: viral, bacterial, and allergic. In most cases, it's caused by a virus, similar to what causes a runny nose or sore throat when you have a cold. Allergies can also cause pink eye, and that form isn't as contagious as the others. Pink eye can also be bacterial, and is often caused by the same bacteria that causes strep throat. Any eye irritant — like smoke, contact lenses, or chemical exposure — can also cause pink eye.

Oh, and if you've heard that you can get pink eye by farting on someone's pillow, that's not necessarily true. But doctors still don't want you touching your mouth or anus and then touching your eye, because you can potentially spread bacteria that could cause conjunctivitis, William Barry Lee, MD, wrote on the AAO website.

The way you treat conjunctivitis depends on which type you have, which is why it's important to see a doctor if you think you have it. Viral conjunctivitis usually goes away after a few days, because your body fights off the infection on its own, according to the AAO. If allergies are behind your pink eye, you can use eye drops to help with the itchiness, and try to avoid your triggers. But bacterial conjunctivitis, on the other hand, usually requires prescription antibiotic eye drops, and will clear up after a few days or in up to two weeks, according to the CDC. Conjunctivitis is generally nothing to worry about, but if it's left untreated, it can impact your vision, according to the Mayo Clinic.

There's one more annoying detail: It can be very contagious. If you have pink eye, anything you touch can spread it, according to the CDC. To prevent pink eye from spreading (or re-infecting yourself), the AAO recommends that you wash your hands before and after you eat, when you use the bathroom, and after you sneeze or cough. You should also use a clean towel or tissue each time you wipe your face and eyes, and try your hardest not to touch your eyes if you have pink eye. Bacteria that causes pink eye can also live on makeup, so the AAO suggests you replace all your eye makeup as soon as you get pink eye (which doesn't sound so bad, tbh). If you wear contact lenses, your doctor might tell you not to wear them while you're treating the infection, or they might give you specific instructions for cleaning them.

You don't necessarily have to post five selfies on Instagram to let everyone know that you have conjunctivitis, but you should tell the people you live with so they don't accidentally get it, too. Of course, there's nothing to be embarrassed about if you do have conjunctivitis — like we said, it's very common. But still, good for Bieber for talking about eye health. Here's hoping that his Instas are the only other things that go "viral."