The appearance of toenails can be an important indicator of systemic disease. Koilonychia is a nail deformity characterized by a longitudinal concavity of the nail plate that creates a “spoon-shape” appearance. This nail deformity is associated with numerous conditions including nutritional deficiencies, genetic disorders, trauma, occupational exposure, vascular disorders, autoimmune disease and musculoskeletal disorders. The most commonly reported cause of koilonychia is iron deficiency anemia.1 In infants, koilonychia is a common, normal variant that results from the thin and soft nature of the nail plate. It is most commonly visible on the infant’s great toes. This deformity typically resolves spontaneously within the first few years of life. In addition to normal infantile koilonychia, several congenital disorders may account for koilonychia in pediatric patients. These disorders include ectodermal dysplasias, trichothiodystrophy, LEOPARD syndrome, Darier’s disease and nail-patella syndrome.2 Familial koilonychias is a rare genetic disease that is not associated with other ectodermal, systemic or orthopedic defects.3 There are several theories regarding the etiology of the nail changes in familial koilonychia including structural stress during the keratinization process of nail formation, lesser angulation of the distal nail matrix in comparison to the proximal nail matrix, and anoxia and atrophy of the nail matrix.4,5 In adults, koilonychia is associated with several acquired disorders including lichen planus, psoriasis, Plummer-Vinson syndrome, Darier’s disease, Raynaud’s disease and lupus erythematosus.6,7 Many of these disorders have an autoimmune basis or subsequently cause iron deficiency. The most common cause of koilonychia is chronic iron deficiency anemia.7,8 Iron deficiency can result from several causes including malnutrition, gastrointestinal bleeding, genitourinary bleeding, worms, malignancy, celiac disease and Plummer-Vinson syndrome.7 Additional disorders of iron metabolism, namely hemochromatosis, reportedly cause koilonychia.1 Authors recommend that when koilonychia is present without an etiologic illness, one should obtain a complete blood count and ferritin labs to rule out iron deficiency and hemochromatosis.7 Environmental factors including high altitude and occupational exposure to petroleum-based solvents are other reported causes of koilonychia. Authors have reported a high prevalence of koilonychia in individuals living at high altitude. Sawhney found that nearly 50 percent of the Indian Ladakhi population who live at an elevation of 3,445 meters had koilonychia.9 The hypothesis is that chronic hypoxia of high altitude causes increased erythropoiesis and depletion of iron stores, leading to thinning of the nail plate and atrophy of the distal nail bed.9 Studies have also reported koilonychia secondary to chronic occupational exposure of hairdressers to petroleum-based products for hair weave and hair removal.10,11 Examination of the toenails can provide evidence of underlying systemic disease. The presence of koilonychia should prompt further workup for an underlying systemic or environmental cause. References 1. Barnett JM, Scher RK, Taylor SC. Nail cosmetics. Dermatol Clin. 1991; 9(1):9-17. 2. Lembach L. Pediatric nail disorders. Clin Podiatr Med Surg. 2004; 21(4):641-650. 3. Prathap P, Asokan N. Familial koilonychia. Indian J Dermatol. 2010; 55(4):406-7. 4. Mittal RR, Dhaliwal MS. Familial koilonychia with superimposed myxoid cyst. Indian J Dermatol Venerol Leprol. 1995; 61(1):63-4. 5. Stone OJ, Maberry JD. Spoon nails and clubbing: Review and possible structural mechanisms. Tex Med. 1965; 16:620-7. 6. Sotiriadis DK. Hair and nail disorders. Expert Rev Dermatol. 2008; 3(6):677-690. 7. Fawcett RS, Linford S. Nail abnormalities: clues to systemic disease. Am Fam Physician. 2004; 69(6):1417-24. 8. Kumar G, Vaidyanathan L, Stead LG. Images in emergency medicine. Koilonychia, or spoon-shaped nails, is generally associated with iron-deficiency anemia. Ann Emerg Med. 2007; 49(2):243, 250. 9. Sawhney MP. Ladakhi koilonychia. Indian J Dermatol Venereol Leprol. 2003; 69(2):79-80. 10. Alanko K, Kanerva L, Estlander T, Jolanki R, Leino T, Suhonen R. Hairdresser’s koilonychia. Am J Contact Dermat. 1997; 8(3):177-8. 11. Pancar GS, Kalkan G. Irritant nail dermatitis of chemical depilatory product presenting with koilonychia. Cutan Ocul Toxicol. 2014; 33(1):87-9.