Dark Spots Under a Toenail: What to Know

A bruise beneath the nail can occur after a knock, tight footwear, or repeated pressure. It generally grows outward as the nail grows, although the nail can take a long time to replace itself. Yellow, crumbly, thickened, or lifting nail can suggest fungal infection. A brown or black band may arise from pigment in the nail unit; pigment can also extend onto the nearby skin. These patterns cannot be identified reliably from colour alone.

Think back to recent injury, new footwear, or nail treatments, and take a dated photograph. Keep the nail trimmed without digging into its sides, protect it from pressure, and avoid trying to drill, bleach, or scrape beneath it. A clinician may examine the nail and surrounding skin and decide whether testing or specialist review is needed. Chemical peels, brightening products, and lasers are not suitable substitutes for diagnosing a nail-unit lesion.

Arrange prompt dermatology assessment if the mark has no clear injury, becomes wider or darker, has an irregular pattern, reaches the cuticle or surrounding skin, or appears in one nail and persists. Seek urgent care for severe throbbing pain, major swelling, pus, spreading redness, or fever after an injury.

Ask whether the mark is moving with nail growth, whether infection testing is appropriate, whether the pigment involves nearby skin, and how soon it should be rechecked.