Why does melanonychia cause discoloured nails?

The nail matrix is the growth area beneath the skin at the base of the nail. When its pigment cells make more melanin, brown or black pigment becomes incorporated into the nail as it grows forward. This can create a stripe, a broader band, or more diffuse colour. Discoloured Nails is a common presentation of Melanonychia. Causes of melanonychia vary and can include normal pigment variation, repeated injury, inflammation, medicines, or changes in the nail unit that need assessment. A single nail with a new or widening band deserves particular attention.

Take a dated photograph of the nail and note whether the band is widening, changing shade, or extending onto the surrounding skin. Avoid biting, picking, aggressive filing, or repeated trauma while it is being assessed. Arrange a dermatology appointment for a new, changing, irregular, or unexplained band. The clinician may examine the nail with magnification and may recommend monitoring or sampling, depending on its pattern and your history.

Seek prompt assessment if pigment affects one nail without a clear explanation, becomes wider toward the base, develops several shades, or spreads onto the cuticle or nearby skin. Arrange earlier care if the nail is painful, split, bleeding, lifting, or associated with a new lump. Urgent help is needed for severe pain, rapidly increasing swelling, or signs of infection.

Ask whether the colour pattern fits melanonychia, what benign causes are possible, whether another nail or skin area should be examined, and how often the nail should be reviewed. Tell the clinician about injury, manicures, medicines, skin conditions, and when the band first appeared.