Fingernails provide subtle clues about our overall health — though they're often either covered in nail polish or overlooked altogether.<br />They're made out of keratin, which is the same material in found in skin and hair.<br />According to Allure, weak and brittle nails are often a sign of deficiencies in iron, or in vitamins B or D.<br />Horizontal ridges can come from physical trauma, but can also indicate malnutrition, psoriasis, or a thyroid problem. See a doctor.<br />A brown, vertical stripe is called melanonychia. While usually benign, it can sometimes indicate melanoma. See a dermatologist immediately.<br />Finally, if one or more of your nails is red, swollen, and infected, go to the emergency room right away.
