Ridges or lines in fingernails can be a sign of a health condition or a previous injury to the nail. Vertical ridges are typically harmless and are a common sign of aging. However, horizontal ridges or dents in the nails, also known as Beaus lines, can be a sign of an underlying condition that requires diagnosis and treatment. Possible causes of horizontal ridges include damage to the nail matrix due to mechanical trauma, dermatological conditions such as eczema or psoriasis, and systemic problems within the body. Other medical disorders that can cause vertical ridges to appear in the nail include trachyonychia, peripheral vascular disease, and rheumatoid arthritis. Nutritional deficiencies, such as iron, folic acid, or protein deficiency, can also contribute to ridges in nails. If you notice a change in your nails, it is important to see a doctor to determine the underlying cause.