Brittle, ridged fingernails. Can be caused simply by injury to the flesh under the nail (as in, having a nail torn off), or can be a symptom of anaemia, iron deficiency. (Very rarely, it can be a symptom of Lychen Planus, an itchy skin disease or Dystrophic Epidermolysis Bullosa, though what that is I don't know and I'm not sure I want to find out.) In most cases it is easily treated either by protecting the wound to the nailbed until it heals over, or in the case of anaemia, by a course of iron supplements.