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.

3. Petroleum Exposure

Exposure of petroleum-containing products to an individual's nails over an extended duration can cause them to develop nail deformities, including koilonychia. The nail bed and nail matrix epithelial cells are both responsible for the formation of the nail plate, nail, and nail bed. The area underneath the nail plate and the nail fold are the most vulnerable areas when it comes to chemical exposure to an individual's fingernails. In the area of its free margin, chemical substances can penetrate underneath an individual's nail plate and nail bed. Most occupations involving exposure to petroleum-containing substances fall under the category of cosmetology, including hairdressers, beauticians, barbers, and nail technicians. Chemicals such as petroleum can also induce a condition called allergic dermatitis in the periungual skin regions, causing repeated inflammation to a patient's nail bed. Any chemical substance that results in an inflammatory response in an individual's nail matrix or nail bed can cause the nail to become distorted or deformed. Precautions should be taken by those who work closely with harsh chemicals that contain petroleum, such as wearing protective gloves on the hands.

4. Higher Altitudes

Koilonychia can be caused by an individual's long-term residence at higher altitudes. The atmospheric air an individual breathes in becomes thinner as they go up in elevation from sea level. While the air technically contains the same 20.9 percent oxygen content at all elevations, the lower pressure at higher elevations decreases the amount of effective oxygen an individual is able to breathe in. For example, the amount of effective oxygen sits at 20.9 percent at sea level, and an elevation of five thousand feet above sea level only yields 17.3 percent effective oxygen. An elevation of ten thousand feet yields a further decreased 14.3 percent oxygen, which falls just below ten percent effective oxygen at an altitude of approximately twenty thousand feet. The body receives less oxygen at high altitudes, making less oxygen available for cells around the body. The body responds by increasing its production of red blood cells, causing a depletion in iron stores and resulting in iron deficiency anemia.

5. Plummer-Vinson Syndrome

A patient's Plummer-Vinson syndrome can cause them to develop koilonychia in their nails. Plummer-Vinson syndrome is a disorder characterized by esophageal webs, chronic iron deficiency, and dysphagia. The cause of Plummer-Vinson syndrome is unknown, and the disorder is a very rare occurrence in the human population. Plummer-Vinson syndrome occurs more often in women than it does in men, but the reasons behind this gender imbalance distribution are unknown. Koilonychia is a characteristic symptom that occurs in some Plummer-Vinson syndrome patients along with the symptoms of glossitis, enlargement of the spleen, and thyroid enlargement. The chronic iron deficiency that occurs in individuals affected by this syndrome is the component connecting it to koilonychia. An insufficient amount of iron provided to the iron-containing enzymes that perform functions in the epithelial cells in and around the nail bed is the best-known mechanism behind iron deficiency precipitated koilonychia.

6. Hypothyroidism

Hypothyroidism, a condition where the thyroid gland underproduces essential hormones, can contribute to the development of koilonychia. The thyroid gland plays a critical role in regulating metabolism and maintaining healthy tissues, including the nails. A sluggish thyroid slows down the body’s ability to repair and regenerate cells, leading to brittle and spoon-shaped nails. Patients with hypothyroidism often experience additional symptoms such as fatigue, weight gain, and hair thinning. The decreased circulation and reduced delivery of essential nutrients to the nail bed in hypothyroid individuals can exacerbate this condition. Treating hypothyroidism with hormone replacement therapy often resolves associated nail deformities over time.

7. Raynaud’s Disease

Raynaud’s disease, a condition characterized by reduced blood flow to extremities due to blood vessel spasms, can lead to koilonychia. This condition commonly affects the fingers and toes, causing them to turn white or blue when exposed to cold temperatures or stress. Chronic episodes of restricted blood flow deprive the nail beds of oxygen and essential nutrients, potentially leading to spoon-shaped nails. Individuals with Raynaud’s may notice other symptoms like numbness, tingling, and a cold sensation in their extremities. Addressing the underlying vascular issues through lifestyle changes or medications to improve circulation can help reduce the likelihood of developing nail abnormalities.

8. Celiac Disease

Celiac disease, an autoimmune disorder triggered by gluten ingestion, can indirectly cause koilonychia. This condition damages the lining of the small intestine, impairing the absorption of essential nutrients such as iron, zinc, and B vitamins. The resulting nutrient deficiencies, particularly iron deficiency anemia, are strongly associated with spoon-shaped nails. Other symptoms of celiac disease include gastrointestinal discomfort, fatigue, and skin rashes. For patients with celiac disease, adhering to a strict gluten-free diet is critical to restoring nutrient levels and promoting overall health, which can improve the appearance of the nails.

9. Chronic Inflammatory Conditions

Chronic inflammatory conditions, such as rheumatoid arthritis and lupus, can lead to koilonychia through systemic inflammation and poor nutrient absorption. These conditions often cause inflammation in blood vessels and tissues, disrupting the delivery of oxygen and nutrients to the nails. Additionally, patients with chronic inflammatory conditions may develop anemia of chronic disease, further contributing to nail abnormalities. Managing the underlying inflammatory condition with medication and dietary adjustments can help alleviate the symptoms of koilonychia over time.

10. Fungal Infections

Fungal infections of the nails, medically termed onychomycosis, can cause changes in nail structure, including koilonychia. Fungal infections often begin as discoloration or thickening of the nail and, if left untreated, may lead to severe deformities. The fungi invade the nail bed and matrix, disrupting the growth of healthy nail tissue. Individuals with compromised immune systems or diabetes are particularly susceptible to fungal infections. Treating the infection with antifungal medications can restore nail health and prevent further complications.

11. Vitamin B12 Deficiency

Vitamin B12 deficiency can contribute to a range of nail abnormalities, including koilonychia. This essential vitamin plays a key role in the production of red blood cells and the maintenance of healthy tissues. A deficiency in B12 leads to megaloblastic anemia, characterized by the production of abnormally large and ineffective red blood cells, which reduces oxygen delivery to peripheral tissues like the nail beds. This can result in brittle, spoon-shaped nails. Including vitamin B12-rich foods, such as meat, fish, eggs, and fortified cereals, or taking supplements can help correct the deficiency and improve nail health.

12. Hemochromatosis

Hemochromatosis, a genetic disorder that causes excessive iron accumulation in the body, can also result in koilonychia. While iron deficiency is a more common cause, the excess iron in hemochromatosis damages tissues and organs, including those responsible for nail health. The condition often leads to brittle, deformed nails due to systemic disruptions in iron metabolism. Other symptoms of hemochromatosis include joint pain, fatigue, and skin pigmentation changes. Managing iron levels through regular blood removal (therapeutic phlebotomy) or medications can help alleviate associated symptoms, including koilonychia.

Understanding Koilonychia Causes

Koilonychia, or spoon-shaped nails, is more than a cosmetic concern—it can be a key indicator of underlying health conditions. From common causes like iron deficiency and fungal infections to more complex factors such as autoimmune disorders, vitamin deficiencies, and genetic conditions, understanding the root cause is essential for effective treatment. This expanded list of 12 potential causes highlights the diverse and sometimes surprising factors that can lead to koilonychia, emphasizing the importance of proper diagnosis and targeted care. While some cases resolve with simple dietary or lifestyle changes, others may require medical intervention to address systemic health issues. By staying informed and seeking timely medical advice, individuals can manage this condition and improve both nail health and overall well-being. Koilonychia serves as a reminder of how closely linked our external appearance is to our internal health, encouraging proactive care and awareness.