Skin Cancer Warning Signs: The ABCDE Rule and When to Get Checked

Part of: Skin cancer & dermatologic surgery

ABCDE melanoma signs, which skin changes need assessment, and the role of dermoscopy and biopsy.

Skin cancer · 2 min read · September 9, 2026

Written and medically reviewed by Dr. Yousef Abo Zarad · German board-certified dermatologist · Last reviewed: September 2026

The short answer

ABCDE helps identify spots that need examination; it cannot diagnose or rule out melanoma. Any changing mole, a spot different from the others, or a sore that does not heal should be assessed by a dermatologist, even when it is small.12

The clinician may use dermoscopy. If melanoma is suspected, diagnosis is confirmed by histopathology, not a phone photo or an app.3

What are the ABCDE signs?

  • A — Asymmetry: one half of the spot does not match the other.1
  • B — Border: irregular, scalloped or poorly defined edges.1
  • C — Colour: several colours within one spot, from shades of brown and black to areas of white, red or blue.1
  • D — Diameter: melanomas are often larger than 6 mm (a pencil eraser), but they can be diagnosed when smaller, so size alone cannot rule cancer out.1
  • E — Evolving: a spot that looks different from the rest or changes in size, shape or colour.1

What other signs call for an examination?

  • A new or changing spot: especially if it differs from other moles, itches, bleeds or becomes painful.12
  • A non-healing sore, a recurring sore or a growing lump that ulcerates.2
  • A new or changing dark streak under a nail or pigmentation extending onto adjacent skin.2
  • Darker skin: examine palms, soles and nails too; melanoma can occur there as well as on sun-exposed sites.2

Who needs closer follow-up?

  • Numerous or atypical moles, previous melanoma, or a strong family history warrant an individualized surveillance plan agreed with a dermatologist.4
  • Self-examination can reveal change, but cannot replace medical assessment of a concerning spot.1

What happens at the dermatologist?

  • Clinical examination: the dermatologist asks when the lesion appeared, whether it changed, and examines it against the rest of the skin.13
  • Dermoscopy: reveals patterns not visible to the naked eye and improves accuracy in experienced hands.3
  • Histopathology: when melanoma is suspected, full-thickness complete excision is generally preferred where feasible, with exceptions for larger or anatomically difficult lesions. See the mole check and biopsy guide.3

What to do now

  • Arrange a prompt skin examination for a changing, newly unusual, bleeding, persistently itchy or painful lesion.12
  • Do not wait until it reaches 6 mm and never attempt removal yourself.1
  • Use reference photos when helpful, and check the back, scalp, nails, palms and soles; ask someone you trust to help with hard-to-see areas.12

Medical Evidence