Careful where you barefoot.

Elephantiasis podoconiosis is caused by repeatedly walking barefoot in volcanic soils, which contain tiny, sharp mineral crystals that can penetrate the soles of the feet. Once these crystals are under the skin, they provoke repeated cycles of inflammation. Over time, the inflammation produces a build-up of scar tissue that blocks lymphatic vessels and produces dramatic and disabling swelling and open sores in the lower legs.

Mysterious outbreak of disfiguring tropical disease in western Uganda linked to decades of walking barefoot in volcanic soils | EurekAlert! Science News