What should you know about dark discoloration on nails?

A bruise may follow pressure or an impact and can move toward the tip as the nail grows. Fungal disease may make a nail thicker, brittle, crumbly, or yellow-brown. Nail psoriasis can cause pitting, lifting, or changes in the nail surface. A dark streak or patch without a clear injury, especially if it changes or extends onto nearby skin, needs dermatology assessment. See [Discoloured Nails](/symptoms/nail-discoloration/) for a broader overview.

Colour alone does not identify the cause. The clinician may inspect several nails, the surrounding skin, and the direction of any streak, while asking about trauma, footwear, manicure products, and skin conditions. Related possibilities include [Nail Fungus](/conditions/nail-fungus/) and [Nail Psoriasis](/conditions/nail-psoriasis/).

Keep the nail trimmed without cutting the surrounding skin, avoid picking or scraping beneath it, and pause harsh manicure products if they irritate. Photograph the change in good light and record whether it moves with nail growth, spreads, or affects other nails. Do not start antifungal medicine based on colour alone; treatment should match an identified cause.

When fungal infection is confirmed, a clinician may discuss [Oral Antifungal Treatment](/treatments/medical-dermatology/oral-antifungal-therapy/). The choice depends on the nail involved, other medicines, health conditions, and examination findings.

Book a dermatology assessment for a new dark streak, a mark that widens or changes, pigment reaching the surrounding skin, unexplained bleeding, pain, swelling, or a nail that lifts without a clear injury. Seek prompt care for signs of infection such as spreading redness, warmth, pus, or fever. A bruise that does not behave as expected as the nail grows also deserves review.

Ask whether the change fits trauma, fungal infection, psoriasis, or another pigment process. Is a nail sample, photograph, or follow-up examination needed? Which products should you avoid, and what change in the streak, nail surface, or surrounding skin should prompt an earlier appointment?