What causes discoloured nails?

Yellow, thickened, crumbly nails may occur with [Nail Fungus](/conditions/nail-fungus/), while green colour can occur with [Green Nail Syndrome](/conditions/green-nail-syndrome/). A brown or black band may be pigment called [Melanonychia](/conditions/melanonychia/), although a single changing band needs careful examination. A dark mark beneath the nail after impact may be a [Bruised Nail](/conditions/subungual-hematoma/), and pits, ridges, separation, or oil-like patches can accompany [Nail Psoriasis](/conditions/nail-psoriasis/). Nail polish, dyes, smoking, medicines, and repeated wet work can also alter colour. The appearance alone cannot reliably identify the cause.

Take a clear photograph and note when the colour changed, whether it is moving outward with nail growth, and whether one or several nails are affected. Keep nails clean and dry, avoid cutting the cuticle, and do not share clippers. Remove polish before assessment. Do not start an oral antifungal medicine based only on colour; a clinician may use examination, a nail clipping, or another test first. Information about [Oral Antifungal Treatment](/treatments/medical-dermatology/oral-antifungal-therapy/) can help you prepare.

Book a medical review for a new dark streak, colour change in one nail without a clear injury, rapid change, pain, swelling, pus, bleeding, nail separation, or skin colour extending around the nail. Seek prompt care if you have diabetes, poor circulation, reduced immunity, or a wound near the nail. A changing pigment band should not be covered with polish while waiting for assessment.

What pattern do you see, and which causes fit it? Do I need a nail sample? Could an injury, medicine, infection, or psoriasis explain the change? Should I stop a product or polish? What changes should make me return quickly?