9 Nail Changes That Can Signal Medical Conditions
1. Spoon-shaped nails (koilonychia): Nails curve upward at the edges, forming a concave spoon shape. One of the most specific physical signs of iron deficiency — a study in the Journal of the American Academy of Dermatology found that koilonychia had a 60 percent positive predictive value for iron deficiency. If your nails are spooning, get your ferritin checked.
2. Pale or white nail beds: Healthy nail beds are pink (blood vessels visible through transparent nail). Pallor indicates anemia (any cause), liver disease (Terry's nails — white with dark band at tip), or kidney disease (half-and-half nails — lower half white, upper half brown). A BMJ study found nail bed pallor had 65 percent sensitivity for anemia.
3. Yellow nails: Most commonly fungal infection (onychomycosis) — nails become yellow, thickened, brittle, and may separate from the nail bed. Affects roughly 10 percent of adults. Less commonly: yellow nail syndrome (rare — yellow nails, lymphedema, respiratory problems). Nail polish and smoking can also stain nails yellow.
4. Horizontal grooves (Beau's lines): Deep horizontal ridges across the nail indicate temporary growth interruption — severe illness, high fever, surgery, chemotherapy, or extreme stress caused the nail matrix to briefly stop producing nail. By measuring distance from cuticle, you can estimate when the disruption occurred (nails grow ~3mm/month). Multiple Beau's lines across all nails suggest a systemic event.
5. Pitting: Small, regular dents across the nail surface. Characteristic of psoriasis (affects up to 50 percent of psoriasis patients and can precede skin symptoms by months or years). Also seen in eczema and alopecia areata.
6. Dark lines under the nail: A single dark longitudinal line can be normal (melanonychia striata — present in up to 77 percent of Black adults). However, a new, widening, or irregular dark line — especially on a single nail — can indicate subungual melanoma. This requires urgent dermatology evaluation. Bob Marley's death from melanoma originating under his toenail illustrates the danger of delayed diagnosis.
7. Clubbing: Fingertips enlarge and nails curve around the fingertips, losing the normal angle at the cuticle. Associated with chronic low blood oxygen — COPD, pulmonary fibrosis, lung cancer, congenital heart disease, inflammatory bowel disease, or liver cirrhosis. New-onset clubbing should always be investigated with chest imaging.
8. Brittle, splitting nails: The most common nail complaint. Usually environmental — repeated wetting/drying, harsh chemicals, nail polish remover. Medical causes: hypothyroidism, iron deficiency, biotin deficiency. A study found that biotin supplementation (2.5mg daily) improved nail thickness and reduced splitting in 63 percent of patients after 6 months.
9. Nail separation (onycholysis): The nail lifts from the nail bed, starting at the tip. Causes: trauma, fungal infection, psoriasis, hyperthyroidism, and allergic reactions to nail products. If multiple nails are affected without obvious cause, thyroid function should be checked.
When to See a Doctor
See a dermatologist if you notice a new dark line under a single nail (possible melanoma), clubbing of fingertips (possible lung or heart disease), sudden changes in multiple nails (possible systemic illness), nail changes with other symptoms (fatigue, weight changes, shortness of breath), or any progressive, unexplained nail change.
Common myth debunked: White spots on nails do NOT indicate calcium deficiency. They are almost always caused by minor trauma to the nail matrix weeks earlier (leukonychia punctata). They are harmless and grow out. No dietary change is needed.
