Infants with iron deficiency have a higher rate of koilonychia--concavity of the outer surface of the nail--(strength of recommendation [SOR]: C, one case-control study). Vitamin B12 deficiency is associated with various nail pigment changes that are reversible with treatment (SOR: C, case reports). Muehrcke's lines (transverse white bands that run parallel to the lunula) occur in a minority of patients with hypoalbuminemia. (SOR: C, one cross-sectional study). Fingernail clubbing has been found in most patients with kwashiorkor, or protein malnutrition (SOR: C, one cross-sectional study). Transplacental exposure to polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs) has been associated with nail deformities and color changes (SOR: C, one case-control study)
