Runners’ feet tend to swell when they run. As the length of the long run increases, I believe that some of the extra fluid migrates into the toe region as the foot slings forward, step after step. During hot weather, the fluid level increases even more. The internal pressure of the fluid against the toenail can allow for fluid buildup between layers of the nail. It is very common for a few blood capillaries to break or leak blood, which produces the red and then black color. Pain can result from the fluid buildup. This can be released with a sterilised needle if it gets too great (see note below).

Aggravating pressure on the toenail are two motions of the toes that seem to be genetic: clawing and rising. These are involuntary motions but put pressure on the outside layer of the nail often causing the hard outside layer to separate from the next layer which is soft. This separation provides a pocket where excess fluid can accumulate.

Here are some ways you can prevent this:

1. When you buy shoes, make sure there’s at least 1.5cm between your longest toe and the front of the shoe, when standing. Wear the same type of sock you use when running.

2. Put foot powder in your socks and shoes to reduce friction.

3. Put a skin lubricant on your toes.

4. Keep your toenails clipped.

5. Wear thinner socks during the warm-weather months.

6. Insert more walk breaks into longer long runs, from the beginning.

7. During warm weather, run during the coolest time of the day.

8. During warm weather, take a 3-to-4-minute “foot soak break” in ice water after every long run.

9. To reduce risk of infection, check with a doctor before performing any release of the fluid. If you do drain the fluid, apply a triple antibiotic cream in and around the drainage point.

READ MORE ON: BLACK TOENAILS injury-prevention