I have a bad case of reef rash. I would post a picture, but it isn’t pretty. It looks like raw hamburger that has been left in the sun.
How did I get it? My shoulder scraped a reef and what would normally be a simple, small scrape, healing in a few days, has become a war of attrition between the white blood cells responsible for attacking foreign bodies in my system and the persistant nematocytes that coral use to protect themselves. So far, the nematocytes are winning and my shoulder, while the scrape itself is almost free of scabbing, is still angry and red.
If you have never had reef rash, I think you should run out to your nearest salt water aquarium, break off a piece of live coral and run it up and down your arm as forcefully as possible. You know, just for the sake of experience and science. We can be reef rash buddies!