Many people indulge in activities, for a livelihood, as well as for recreation and relaxation, which can hardly be performed without getting one's hands dirty.  For example, in gardening, it is often necessary for one to manipulate the soil in one way or another, causing the soil to be caked under one's fingernails.  In most cases, the dirt and/or soil can be removed from the hand simply by washing with soap and water, but it is considerably more difficult to remove the soil from under the nails.  In addition to the removal of dirt, there are many professions, such as medicine where it is necessary to keep the hands and nails free of bacteria, whether or not the presence of dirt is apparent.