A skin indention at the lower back of a human body is called as Pilonidal Dimple. These are found just above the buttocks and are very small and shallow. These are generally found during the time of birth. Sometimes these are accompanied with increased growth of hair in this area and no causes are found for these dimples to happen. These are normally harmless but if these dimples are large, tender, swollen or full of fluid then this can reveal serious abnormality which may involve the spine or the spinal cord. Infection of these dimples can turn into cysts and may need surgical help.