This is a common problem in running. I have had black toes several times, mostly on long runs (>10 miles). First you need to make sure you keep your toenails cut short and make sure you have a wide enough toe box. I have been told that even with the proper precautions you can still get these. After I ran the Houston this past fall, I had a bad one. I stuck a needle under my toenail to relieve the pressure, but that is your choice.Your toenail will usually come off weeks later.

This sounds painful but you don't feel anything, trust me. Take a hot needle and put it over your black nail. spin it until it breaks the nail ever so slightly. the blood will seep out and all the pressure will be gone.

I have a nice one... first a got a blood blister on the tip of my toe then under the toenail. I was unable to bleed out the under the toenail blister so now it's lifing off. Very nice to look at...

This started when I started to increase my mileage. Similar to aggiedvm, consistant runs over 10 miles got me. Upto that point I'd never had such issues wearing the same size shoes. It does seem to depend on the shoe. My Kayano 13s were offender. My DS Trainers are fine. I'll size up if I get another pair of Kayanos.

I had black toenails on my second toes, which are longer than my big toes. When I went to buy new shoes (at a running store) I told the salesperson I wanted a 1/2 size larger to prevent it from happening again. She assured me that a bigger shoe wouldn't make a difference with long distances. The pain went away after a few days, and a black line remained until the nail grew completely out about 6 mo later. Never lost one!