Disclaimer: this might be a bit icky, so don't read if you're not prepared to read about toes, feet, blisters, and other running injuries.
I've heard of the "black toenail" syndrome and people who develop horrifying blisters from their running. Perhaps I am lucky, but neither have ever been a problem for me before. My luck ran out last week when I started noticing tenderness of the nail bed of one of my small toes on the right foot. On closer examination it appeared that I had developed a blister underneath the toenail and there was some separation of the nail from the bed.
Last night, I was trimming nails when it, well, popped. Ew. Gross. Blisters. Nasty. Yes. Well, I bandaged it, a little ointment, and ran on it this morning fine with no pain.
My first google search for "running" and "toenail" turned up 212,000 results. For the uninitiated, the condition known as "black toenail" refers to blood that collects in a blister under or near the toe making the nail appear discolored. Many advocate draining the blister, especially if it is painful and simply applying antibiotics and letting it grow out/fall off, including running legend Jeff Galloway. Galloway has a great article on the condition. In it, he mentions hot weather and sweaty feet being a potentially increased risk, which has DEFINITELY been the case running in Florida (see my other posts complaining about the humidity).
Anyway, mine's doing okay now and suprisingly doesn't hurt hardly at all. I am considering some new apparel though.