12 Surprising Causes of Spoon-Shaped Nails (Koilonychia)

Koilonychia, also known as spoon-shaped nails, is a condition where the nails develop a concave, spoon-like appearance. Initially presenting as unusually flat nails, this deformity is most often noticed in the fingernails rather than toenails. Over time, the nails soften, and the indentation in the center becomes prominent enough to hold a droplet of liquid. While koilonychia is common in infants and often resolves on its own, its presence in adults may signal an underlying health issue that requires attention. Treatment typically depends on identifying and addressing the root cause, such as environmental, nutritional, or medical factors. Genetic cases may not be preventable, but many instances linked to lifestyle or nutrition can often be treated or even avoided altogether. In this expanded list, we explore 12 potential causes of koilonychia, shedding light on the surprising factors behind this unique nail condition.

1. Iron Deficiency

The most prevalent cause of koilonychia is a deficiency of iron in an affected individual's body. Iron deficiency occurs most commonly in children and childbearing-aged women. Any of numerous medical issues can cause an individual to develop an iron deficiency. This condition can be the result of an insufficient amount of iron in an individual's diet. A patient may not be able to properly absorb a sufficient amount of iron from the food they consume. Individuals who live in a region plagued with malnutrition and famine also develop iron deficiency easily. Any individual who experiences a bleed in their intestine may develop a deficiency in iron. Patients affected by and being treated for numerous types of cancer also tend to develop iron deficiency anemia. The exact mechanism of which a lack of iron causes the development of koilonychia is not clear, but it is known to be associated with iron deprivation to iron-containing enzymes in the patient's epithelial cells.

2. Lichen Planus

Patients affected by lichen planus may develop koilonychia as a result of their chronic inflammatory skin condition. Lichen planus causes an affected individual to develop a non-infectious, itchy rash on the skin of their legs and arms. This rash is characterized by purple or pink bumps or lesions that are flat on top, small, and have multiple sides to them. Lichen planus most commonly manifests in individuals who have reached at least their third decade of life. Lichen planus can be caused by certain inherited genetic factors, but in most cases, the cause is idiopathic or unknown. Changes in the nails of which include koilonychia have been observed in approximately ten percent of patients affected by this inflammatory skin condition. The immune-mediated inflammation that occurs in individuals affected by lichen planus can cause their nail matrix to become permanently damaged or destroyed. This mechanism can result in the development of many dystrophies of the nails, including twenty-nail dystrophy of childhood and koilonychia.