Why Do Fingernails Split Down the Middle?
Split fingernails, known as onychoschizia or lamellar dystrophy, are caused by frequent wetting and drying of the hands, exposure to cosmetics and chemicals, injury or malnutrition. According to Skinsight, people whose professions require them to wash and dry their hands frequently are at greater risk of developing onychoschizia. When combined with longitudinal splitting of the nail, the condition can be referred to as brittle nail syndrome.
Although split fingernails can be unsightly, Skinsight considers them largely a cosmetic issue. The only oral treatment for split fingernails is a biotin supplement. In order to prevent split fingernails, recommendations include wearing thin gloves when doing housework, avoiding wetting the hands, keeping the nails as dry as possible and applying petroleum jelly in order to increase nail hydration. Hardening agents should be used with caution and applied only to the growing edge of the nail because they cause brittleness.
In some cases, nail splitting can be a symptom of skin diseases such as psoriasis or lichen planus or a side effect of a medication containing vitamin A. Caring.com also warns that brittle nails can result from a lack of moisture being delivered to the nails, signaling the disruption of metabolic functions as a result of thyroid disease.