How do you tell if a mole is cancerous?
Last updated September 3, 2026.
Use the ABCDE check: Asymmetry, irregular Border, varied Color, Diameter over 6mm, and Evolving - any change in size, shape, color, or new bleeding or itching - plus the ugly-duckling rule: a mole that looks different from all your others. Most moles are harmless and plenty of moles are normal; the check exists to catch the changing outlier. Anything flagged deserves a prompt skin check - a biopsy takes minutes, and melanoma caught early is highly treatable while waited-on melanoma is not. Do a monthly head-to-toe check, including scalp, soles, and between toes. Pymander is a free AI doctor, 24/7 by text, and can help you think through a change.
What to do
- Run ABCDE on any mole that catches your eye: change is the loudest signal.
- Apply the ugly-duckling test: the mole unlike the rest earns a look even without ABCDE signs.
- Photograph with a ruler for scale: comparing over weeks beats memory.
- Book promptly when flagged: early melanoma treatment is a completely different story from late.
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