The body hair of surgical patients may be removed before surgery. In the past, this may have been achieved by shaving, but that is now considered counter-productive, so clippers or chemical depilatories may be used instead. The shaving of hair has sometimes been used in attempts to eradicate lice or to minimize body odor due to accumulation of odor-causing micro-organisms in hair. Some people with trichiasis find it medically necessary to remove ingrown eyelashes. Shaving against the grain can often cause ingrown hairs.