Spoon-shaped nails (koilonychia)

Koilonychia, or spoon-shaped nails, describes nails that have become abnormally thin and soft and curve upwards at their edges, giving the nail a concave, scooped-out shape — the classic test is that the depression could hold a drop of water. It is a specific and well-recognised physical sign, and its most important association in adults is iron deficiency: long-standing low iron, with or without anaemia, can soften and reshape the nails in this way, so spoon-shaped nails are a visible clue that iron stores may be depleted. It usually develops gradually and affects several nails. Other, less common causes exist: it can occasionally be linked to iron overload (haemochromatosis), certain other medical or nutritional conditions, repeated trauma or exposure to solvents and, rarely, it runs in families or is normal and temporary in infancy. But because iron deficiency is by far the most important and treatable cause, spoon-shaped nails in an adult should prompt a check of iron status. When the underlying deficiency is corrected, the nails usually recover their normal shape over months as they grow out.

• Iron deficiency — the classic and most important cause in adults, with or without anaemia.
• Iron-deficiency anaemia — spoon nails may accompany it.
• Iron overload (haemochromatosis) — less commonly associated.
• Repeated trauma or solvent exposure — occupational or mechanical causes.
• Rarely, inherited or normal in infancy — spoon-shaped nails can be temporary in babies.
• Certain other nutritional or medical conditions.

Spoon-shaped nails in an adult are a recognised sign of possible iron deficiency, so the key investigation is iron status: ferritin (the store of iron), a full blood count to look for anaemia and small red cells, and often iron and transferrin saturation. If iron is low, treating it usually allows the nails to grow back normally over months, which both explains the sign and resolves it. Because spoon nails can, less commonly, reflect iron overload rather than deficiency, the iron studies also help distinguish these opposite states. Where iron is normal, other causes and the broader context are considered. Mediora.AI can surface a low-iron (or, less often, an iron-overload) pattern from your results that fits with spoon-shaped nails, helping connect the visible sign to a treatable cause; the interpretation belongs with your doctor.