Curved or tunnel-shaped toenails, also known as hyperconvex toenails, are a common problem in adults. This abnormality occurs when the nail loses its normal arch shape and takes on a curved or tunnel-like shape. This can be painful and lead to irritation and infection. It can also lead to nail deformation and loss of aesthetic appearance.
There are several causes for hyperconvex toenails, including hereditary predisposition, old age, weakened nail beds, and changes in the shape of the foot. Treatment varies depending on the cause and includes wearing comfortable shoes, orthopedic insoles, nail braces, and in some cases, surgery.