A split fingernail is commonly characterized by vertical splitting at the free edge of the nail or by the layers of the nail separating at the edge. The medical term for a split fingernail is onychoschizia, and it is a common nail problem, especially for women. Split fingernails usually are dry and brittle and sometimes have vertical ridges. The most common cause of the condition is thought to be repeated and prolonged contact with water, causing dehydration of the nail by robbing it of the natural moisture and oils that it needs to stay strong and flexible. Only rarely are split fingernails caused by medical conditions or vitamin deficiency.
The fingernail, also called the nail plate, consists of compressed layers of dead cells, just like hair and skin. These layers are kept together by the moisture and oil released by the nail bed, the skin beneath the nail plate. If something interferes with this process, the nail becomes more prone to splitting. For example, as a person ages, the nail bed naturally dries out, making fingernail ridges more common and prominent and increasing the risk of suffering a split fingernail. Contact with water or certain chemicals — even regular soap or the acetone in some nail polish removers — also can interfere with the natural moisture of the nail, causing it to split.
Another cause of split fingernails is nail fungus, a condition that can make the nail plate separate from the nail bed and that sometimes requires medical treatment. Any nail bed injury can also cause a split fingernail. It is important that the entire nail is protected, not just the edge, to avoid split fingernails, because any trauma to the nail bed or the nail plate might show up as a split fingernail when the nail grows out.
Good fingernail care is essential to maintaining healthy nails and avoiding split fingernails as well as other nail problems. Recommended care includes keeping nails dry by using rubber gloves when washing dishes and doing other kinds of cleaning, as well as applying moisturizers such as hand lotion or cuticle oil to the nails. Other suggested measures to prevent split fingernails include limiting manicures, keeping nails short and minimizing the use of nail polish removers, especially those containing acetone. Nail polish removers can be harmful to nails, but nail polish can help strengthen them and can be used to repair an already split fingernail. In addition to these and other forms of external nail care, there is some evidence that taking biotin, a B-complex vitamin, might help strengthen fingernails and prevent them from splitting.