Over the years, I've personally experienced and heard stories about all kinds of embarrassing situations. So here are answers to questions about the most common embarrassing and sensitive topics for runners.
Some runners, especially those training for long-distance events, can suffer from black toenails. It's actually easy to prevent this unsightly problem.
Symptoms: First, the toenail appears blackened (caused by bruising under the nail), and then it eventually falls off.
Causes: Black toenails are caused by constant rubbing of your toe against the front of your shoe. A blood blister forms under the nail, and the blister can't breathe, so it takes a lot longer to heal. Marathoners or runners who do a lot of downhill running are the most likely candidates for black toenails. You're more likely to get black toenails if you run in warmer weather because your feet swell more when it's hot.
Prevention: Make sure that you're wearing the correct sneaker size (at least 1/2 size bigger than your street size; you should have plenty of room in the toebox), trim your toenails, and keep your feet as dry as possible during runs. It helps to wear good wicking socks, not cotton ones.
Treatment: It's best to leave a black toenail alone, as long as the pain is manageable. The pain is usually worst on the first day and then lessens each day after. The damaged part of the nail is gradually pushed off, and a new nail will replace it. Don't force the old nail off -- it will fall off on its own. If you notice redness and infection, see a doctor.