A person’s fingernails can reveal a lot about their health. Most often, fingernail lines are harmless. However, some lines could reveal health problems such as diabetes, thyroid disease, nutrient deficiencies, and more. Lines can run horizontally or vertically and be accompanied by other deformities like discoloration, thickening, and pitting, depending on the underlying disease. Here’s what you need to know about the lines in your fingernails.