GMC-Registered · UK skin cancer specialist
Dermatologist's quick take
- ABCDE = Asymmetry, Border, Colour, Diameter, Evolving
- Evolving (E) is the single strongest melanoma signal — any change matters
- ABCDE misses ~10–15% of melanomas (especially nodular and amelanotic types)
- The 'ugly duckling' sign complements ABCDE: any mole that looks unlike its neighbours
- Photograph suspicious moles monthly — change is what dermatologists look for
I'm Dr. Iwasa, a GMC-registered dermatologist working in UK hospital and private practice. Over the past decade, the ABCDE rule has been the single most important screening tool I teach patients — because melanoma caught early is one of the most curable cancers, and melanoma caught late is one of the deadliest.
In this guide I'll break down each letter, show you the limitations clinicians hold in mind, and explain how to use ScanSkinAI's AI mole check between dermatologist visits. For the wider context, see the rest of the Ask a Dermatologist cluster.
The five letters, explained
A — Asymmetry
Draw a line through the middle. Benign moles match on both sides; melanomas usually don't.
B — Border
Healthy moles have smooth, well-defined edges. Notched, scalloped, or blurred borders are concerning.
C — Colour
One uniform shade is reassuring. Multiple colours — brown, black, red, white, blue — signal risk.
D — Diameter
Most melanomas are larger than 6 mm (pencil eraser) when diagnosed, but small melanomas exist.
E — Evolving
Any change in size, shape, colour, elevation, or symptoms (itch, bleed, crust) is the strongest signal.
+ Ugly Duckling
Any mole that looks distinctly different from your other moles deserves a closer look.
Why 'E' matters most
Of all five letters, Evolving is the one I weigh most heavily in clinic. A mole that has looked the same for 30 years is almost always benign, even if it has irregular borders. A mole that changed in the last 6 months — even subtly — needs evaluation. This is why monthly photographs (or AI tracking) are so powerful: change is invisible day to day but obvious side by side.
What ABCDE misses
Two important melanoma subtypes evade the rule:
- Nodular melanoma grows downward (vertically) from the start. It can be symmetrical, well-bordered, and uniform in colour — but it's the most aggressive type. Watch for any rapidly growing bump.
- Amelanotic melanoma lacks pigment. It looks like a pink or red bump that doesn't heal, often mistaken for a pimple, scar, or insect bite.
For these, the EFG rule complements ABCDE: Elevated, Firm to touch, Growing for over a month.
The ugly duckling sign
Most people have a "family" of moles that all look similar. Melanomas tend to look different from that family — darker, larger, or oddly shaped. When I scan a patient's back, I'm pattern-matching: anything that breaks the pattern earns a closer look. You can do the same in a mirror.
How to do a thorough self-check (10 minutes, monthly)
- Strong, even light. Daylight near a window is better than overhead bulbs
- Full-length mirror plus a hand mirror for the back, scalp, and behind ears
- Check soles of feet, between toes, palms, under nails, and genital area
- Use a phone to photograph any new or changing mole — date the image
- Compare side-by-side with last month's photos. Subtle change is what you're looking for
- If you can't see clearly (back, scalp), ask a partner or use a dermatologist visit
See a dermatologist within 4 weeks if any of these apply
- A mole has changed shape, colour, or size in the last 3 months
- Any new mole appearing after age 40
- A pigmented spot under a fingernail or toenail (especially with a dark streak)
- A non-healing pink bump that bleeds or crusts
- A mole that itches, bleeds, or is painful
- You have a personal or family history of melanoma
Skin of colour considerations
In darker skin, melanoma most often appears on the soles, palms, under nails, and inside the mouth — not sun-exposed areas. The ABCDE rule still applies, but the search pattern is different. Bob Marley died of acral melanoma under his toenail. For more on this, read skin cancer in dark skin.
How AI fits into mole monitoring
A free AI mole check at ScanSkinAI gives you a second opinion in 60 seconds, applies ABCDE/EFG analysis automatically, and stores a dated record so you can spot evolution over time. AI does not replace biopsy — but it does help you decide when a dermatologist visit is warranted, and provides photographic evidence to bring to that appointment.
Check any mole in 60 seconds
Upload a clear photo and get an instant ABCDE-based AI risk assessment.
Frequently Asked Questions
Dr. Celina Kazumi Iwasa
VerifiedGMC-Registered · UK Hospital + Private Practice · Skin Cancer Screening Specialist
Dr. Iwasa is a GMC-registered dermatologist working across UK hospital and private practice settings. She specialises in skin cancer screening, mole assessment and dermoscopy, with a focus on UK and European patients across Fitzpatrick I–IV skin types.