Quick summary of some googling about pinkeye. (I am not a doctor, this is not medical advice.)

What is it?

Pinkeye is not a single disease, it refers to an inflammation of the membrane around your eye. This lack of specificity is surprisingly common in medicine. Any time the Latin name ends in “-itis”, which means “disease of”, you are probably dealing with a similar situation. Pinkeye is also known as conjunctivitis.

Pinkeye can be caused by an infection, either viral or bacterial. It can also be a reaction to allergens, chemicals in the eye, or foreign bodies. Usually we are worried about the infectious forms, because they are contagious.

How bad is it?

In most cases it’s a bit annoying, may cause mild discomfort for 2-5 days, but there is a lot of variability. It can be caused by many different viruses and bacteria. Viral cases in particular tend to have other symptoms. Often these are respiratory. But pinkeye can also be caused by gonorrhea or chlamydia infections, where it is much more likely to have serious effects on your vision.

How common is it?

Welcome to the Hall of Terrible Citations at the Replication Crisis Museum. Wikipedia claims that 6 million Americans get it each year citing a 2013 JAMA paper. That paper in turn cites this 2008 one in The American Journal of the Medical Sciences, which says: “Previous calculations indicated that there were approximately 6 million cases of acute conjunctivitis in the United States each year.” For that, they cite their own unpublished working paper!

“Schneider JE, Chang S, Udeh B, et al.Prevalence and Costs of Conjunctivitis in the Commercially Insured Market.Working Paper in Review.Morristown, NJ: Health Economics Consulting Group LLC; 2007”.

I emailed two of the authors to ask them for a copy of the paper, so we’ll see.

Wikipedia also makes the claim that it accounts for 1% of primary care visits. The citation is to this 1991 paper, which is based on a survey of primary care doctors. They find about 2% of complains are eye-related, and 54% of these are diagnosed with “conjunctivitis and corneal abrasion”. Unless corneal abrasion is part of conjunctivitis, this claim seems overstated.

How contagious is it, and what should you do when you get it?

According to the Mayo Clinic’s factsheet both types are “very contagious”, but also:

Keep in mind that pink eye is no more contagious than the common cold. It’s okay to return to work, school or child care if you’re not able to take time off — just stay consistent in practicing good hygiene.

This is a bit weird, isn’t the common cold very contagious?

The CDC says:

If you have conjunctivitis but do not have fever or other symptoms, you may be allowed to remain at work or school with your doctor’s approval. However, if you still have symptoms, and your activities at work or school include close contact with other people, you should not attend.

Overall, we as a society are becoming more careful about infectious disease transmission, and we should have norms that people with contagious diseases should stay home.