Yellow toenails: causes and what to do

Summary

Fungal yellowing typically affects one or two nails, starts at an edge, and comes with thickening and crumbling. Staining is even, affects many nails, and files away. Yellow nail syndrome is rare and involves slow-growing, curved nails, often with swelling of the legs or chest symptoms.

Common causes

Work through these in order of likelihood.

• Fungal infection — uneven, thickened, debris beneath the nail
• Dark nail varnish worn continuously without a base coat
• Smoking — mostly fingernails, stains the nail surface
• Nail psoriasis — pitting and oil-drop patches alongside yellowing
• Age — nails naturally yellow and thicken after 60

Diagnosis

If clipping the free edge produces crumbly debris rather than a clean cut, infection is very likely. Nail clippings sent for microscopy give a definite answer and are worth requesting before oral treatment.

Treatment options

Staining fades once the cause is removed and the nail grows out. Confirmed infection needs either removal of the diseased nail or a prolonged course of antifungal treatment; the thicker the nail, the less likely a paint-on lacquer is to reach the fungus.

When to seek medical advice

Seek advice if all twenty nails yellow together, if nails stop growing, or if yellow nails appear alongside swollen ankles or a persistent cough.