The Bottom Line

Spoon nails, medically called koilonychia, are nails that have lost their normal gentle downward curve and instead curve upward, forming a concave shape like a spoon. The nail edge lifts up so much that a water droplet placed on the nail would sit without rolling off. Iron deficiency anemia is the most common cause in adults, but spoon nails can also indicate thyroid disease, hemochromatosis, or other systemic conditions. They can also be completely normal in infants. Treating the underlying cause usually allows nails to return to normal shape over several months.

What Are Spoon Nails (Koilonychia)?

A normal nail curves gently downward from the cuticle to the tip, following the shape of the fingertip beneath it. In koilonychia (pronounced koy-loh-NIK-ee-ah, from the Greek for hollow nail), this curve is lost and then reversed — the nail becomes flat and eventually concave, with edges that turn upward. In classic advanced koilonychia, you can balance a drop of water on the nail surface without it rolling off — this is sometimes used as a clinical test.

The condition usually affects the fingernails, particularly the index and middle fingers, though it can involve all fingernails and, less commonly, toenails. It is rarely painful by itself. The nails are often thin and may be brittle.

What Do Spoon Nails Look Like?

The progression from normal to spoon nail has distinct stages:

  • Early stage: The nail looks unusually flat — the normal convex arch is gone
  • Intermediate stage: The center of the nail appears slightly concave, like a shallow dish
  • Advanced stage: The edges of the nail curl upward clearly, forming a deep spoon or cup shape. The nail may be thin and soft

Unlike clubbing (where fingertips also enlarge), spoon nails do not change the shape of the fingertip itself — only the nail plate is affected. Unlike nail pitting (shallow dents), the change in koilonychia involves the overall shape of the nail rather than surface texture.

What Causes Spoon Nails?

Iron Deficiency (Most Common)

Iron deficiency — with or without frank anemia — is the single most common cause of koilonychia in adults worldwide. The nails require iron-containing enzymes for normal keratin synthesis. When iron is depleted, the nail's structural integrity is compromised and it loses its normal shape. Studies have found koilonychia in up to 5.4% of patients with iron deficiency anemia. Associated symptoms often include fatigue, pale skin, shortness of breath, and brittle hair.

Hemochromatosis

Interestingly, the opposite extreme — iron overload from hemochromatosis — can also cause koilonychia. This inherited condition causes the body to absorb too much iron, depositing it in organs including the skin and nails.

Thyroid Disease

Both hypothyroidism (underactive thyroid) and hyperthyroidism can alter nail growth and structure, sometimes producing spoon-shaped nails alongside other nail changes such as onycholysis, brittleness, or slow growth.

Other Systemic Causes

  • Raynaud's phenomenon: Repeated episodes of reduced blood flow to the fingers can affect nail nutrition
  • Celiac disease: Malabsorption of iron and other nutrients can produce koilonychia
  • Lupus
  • Reactive arthritis
  • Hemolytic anemia
  • Plummer-Vinson syndrome: A rare combination of iron deficiency anemia, difficulty swallowing, and koilonychia

Occupational and Chemical Exposure

Prolonged exposure to petroleum solvents (among oil refinery workers and mechanics) can chemically soften the nail plate and cause koilonychia. This occupational form resolves when the exposure stops.

Physiological (Normal in Infants)

Koilonychia in infants and toddlers — particularly affecting the toenails — is usually physiological and resolves on its own by age 3-4 without any treatment or investigation. The nails in young children are naturally thin and soft, and the concave shape typically self-corrects as the nails thicken with age.

Idiopathic and Familial

Some people develop koilonychia without any identifiable underlying cause. A familial form with autosomal dominant inheritance has also been described.

How Is It Diagnosed?

Your dermatologist will examine the nails and ask about symptoms of underlying conditions. Blood tests are the mainstay of workup and typically include:

  • Complete blood count (CBC)
  • Serum iron, ferritin, and total iron-binding capacity (TIBC)
  • Thyroid function tests (TSH, free T4)
  • Sometimes: celiac antibodies, antinuclear antibody (ANA) for lupus

The clinical history is important — ask yourself whether fatigue, cold sensitivity, hair loss, or gastrointestinal symptoms have accompanied the nail changes.

Treatment

Treatment depends entirely on the underlying cause:

Iron Deficiency

Oral iron supplementation (ferrous sulfate is most common) typically produces measurable improvement in symptoms within 4-8 weeks, though nail shape improvement takes longer — usually 3-6 months, following the natural nail growth cycle. The dose and duration are guided by blood test results. The cause of the iron deficiency (dietary, malabsorption, blood loss) must also be identified and addressed.

Thyroid Disease

Normalizing thyroid hormone levels with appropriate medication usually results in gradual improvement in nail changes.

Occupational Exposure

Removing the chemical exposure is the only necessary treatment; nails typically normalize within months.

Nail Care During Recovery

While nails are recovering, keep them short to reduce the risk of the edges catching and tearing. Biotin supplements are sometimes used to support nail strength, though evidence for their effect on koilonychia specifically is limited. Avoid harsh nail chemicals and prolonged water immersion.

When to See a Dermatologist

  • You notice your nails curving upward or looking unusually flat or concave
  • Nail changes are accompanied by fatigue, pale skin, shortness of breath, or cold hands
  • You have been told you are anemic and also notice changes in your nails or hair
  • Your child has persistent spoon-shaped nails beyond age 4-5
  • You have a family history of hemochromatosis and notice nail changes
  • Nail changes appeared after starting a new job involving chemical solvents

Frequently Asked Questions

Is koilonychia the same as nail clubbing?

No — they are different findings. Clubbing involves an increased angle between the nail and the proximal nail fold, along with enlargement and rounding of the fingertip. Clubbing is associated with lung disease, heart disease, and inflammatory bowel disease. Koilonychia is a concave nail shape associated with iron deficiency and other conditions. A doctor can easily distinguish the two on examination.

Can diet alone cause spoon nails?

Yes — a diet very low in iron (common in vegetarian and vegan diets without adequate planning) can cause iron deficiency significant enough to produce koilonychia. Dietary iron counseling and supplementation can resolve it.

Will my nails look normal again after treatment?

In most cases, yes. If the underlying cause is treated, nails grow back with a normal shape as they are replaced from the matrix. The process takes several months because nails grow slowly — about 3 mm per month for fingernails. Toenails take over a year to fully replace.

Do I need to see a specialist, or can my primary care doctor handle this?

Your primary care doctor can order initial blood tests and start treatment for iron deficiency. A dermatologist is useful if the diagnosis is unclear, if the nails are not improving with treatment, or if multiple nail changes are present. If thyroid or gastrointestinal disease is suspected, appropriate specialist referrals may be needed.

  1. Haber R, Khoury R, Kechichian E, Tomb R. Koilonychia: an updated review. Int J Dermatol. 2016;55(11):1201-1207.
  2. Fawcett RS, Linford S, Stulberg DL. Nail abnormalities: clues to systemic disease. Am Fam Physician. 2004;69(6):1417-1424.
  3. Moossavi M, Scher RK. Nail signs of systemic disease. Dermatol Clin. 2006;24(3):293-305.
  4. Baran R, Dawber RPR. Diseases of the Nails and Their Management. 3rd ed. Blackwell Science; 2001.

Trusted Resources

Always consult a board-certified dermatologist for an accurate diagnosis and personalized treatment plan. This article is for educational purposes only and does not replace professional medical advice.