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Red or Black Specks Under Fingernails: Causes & When to Worry

Dark streaks or spots under the nail (subungual pigmentation) have several causes, ranging from benign trauma to melanoma. Prompt evaluation distinguishes harmless from serious conditions.

Common Benign Causes

Subungual Hematoma

  • Mechanism: Trauma (crush injury, dropped object, tight shoes) ruptures nail bed capillaries.
  • Appearance: Dark red, purple, or black discoloration; often painful initially.
  • Progression: Grows out with nail over weeks-months; proximal margin remains fixed.
  • Management: Ice, elevation, NSAIDs. Trephination (drainage) if acute, painful, <24-48 hours.

Splinter Hemorrhages

  • Appearance: Thin, linear red-brown streaks parallel to nail growth.
  • Causes: Minor trauma, nail biting, manicures; also systemic (endocarditis, vasculitis, trichinosis, antiphospholipid syndrome).
  • Significance: Multiple nails or recurrent → investigate systemic causes.

Melanonychia Striata (Longitudinal Melanonychia)

  • Benign: Racial melanonychia (common in darker skin types), pregnancy, medications (minocycline, zidovudine, psoralens), Addison's disease, Laugier-Hunziker syndrome.
  • Nevoid: Localized melanocytic hyperplasia.

Concerning Causes

Subungual Melanoma

  • Warning signs (Hutchinson's sign): Pigment extending onto proximal nail fold/cuticle.
  • ABCDEF rule: Age 50-70, Band >3mm or widening, Change in band, Digit involved (thumb, hallux, index), Extension to skin, Family/personal melanoma history.
  • Dermoscopy: Irregular lines, micro-Hutchinson sign, granular pattern.
  • Action: Urgent dermatology referral for biopsy.

Other Malignancies

Squamous cell carcinoma (often ulcerated, bleeding), metastatic deposits (rare).

When to See a Doctor

  • New pigmented band without known trauma
  • Band widening, darkening, or becoming irregular
  • Pigment on proximal nail fold (Hutchinson's sign)
  • Multiple nails affected without clear cause
  • Associated nail dystrophy, ulceration, bleeding
  • Personal/family history of melanoma
  • Immunosuppression

Diagnostic Approach

  1. History: trauma, medications, systemic symptoms
  2. Dermoscopy (non-invasive, high accuracy)
  3. Biopsy if melanoma suspected (nail matrix biopsy)
  4. Imaging if advanced disease suspected

Most subungual pigmentation is benign, but melanoma must be excluded. Early detection saves lives and nails.

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