Quick Answer
The ABCDE rule checks five warning signs: Asymmetry, Border irregularity, Color variation, Diameter >6mm, and Evolution (change over time). If a mole shows any of these signs, get it checked by a GP or dermatologist. According to Cancer Research UK, almost everyone diagnosed with stage 1 melanoma in England survives 5 years or more — early detection matters.
Melanoma is the most dangerous form of skin cancer, but it's also highly treatable when caught early. The ABCDE rule is a simple, evidence-based method developed by dermatologists to help identify moles that may be melanoma.
By learning these five criteria — Asymmetry, Border, Color, Diameter, and Evolution — you can perform regular self-examinations and know when to seek professional evaluation. Early detection can be lifesaving: Cancer Research UK reports almost 100% 5-year survival for stage 1 melanoma in England, with outcomes worsening sharply at later stages.
Below, we walk through each criterion with clear visual descriptions of what a normal mole looks like versus what should raise concern — so you can apply the ABCDE rule to your own moles today.
The Five ABCDE Criteria — With Visual Examples
Asymmetry
One half of the mole doesn't match the other half
A round or oval mole where both halves look mirror-like — draw an imaginary line down the center and the two sides are nearly identical in shape, size, and color.
One side is clearly larger, shaped differently, or has a different color pattern than the other. The mole looks 'lopsided' — as if one half grew faster or differently.
Draw an imaginary line through the center of your mole. In a healthy mole, both sides should look roughly the same. If one half is noticeably different in shape, size, or color from the other, this asymmetry is a warning sign.
Melanomas are often asymmetrical because cancerous cells grow unevenly.
Border Irregularity
Edges are ragged, notched, blurred, or uneven
A mole with smooth, crisp, well-defined edges — you can clearly see where the mole ends and normal skin begins. The outline is even all around.
Edges that look scalloped, notched, or blurry. The border 'bleeds' into surrounding skin with finger-like projections. Some parts are sharp while others are fuzzy.
Normal moles typically have smooth, well-defined borders. Concerning moles may have edges that are scalloped, notched, or blurry—appearing to 'spread' into surrounding skin.
Irregular borders can indicate that melanoma cells are spreading into normal tissue.
Color Variation
Multiple colors present within the same mole
A single, uniform shade of tan or brown throughout the entire mole. The color is consistent from center to edge.
A patchwork of different shades — dark brown mixed with black, areas of reddish-pink, whitish or grayish patches, or blue-black regions. The colors aren't evenly distributed.
Healthy moles are usually one uniform shade of brown. Melanomas often contain multiple colors—combinations of brown, tan, black, red, white, or blue within the same lesion.
Color variation suggests different rates of abnormal cell growth.
Diameter
Larger than 6mm (about the size of a pencil eraser)
Most benign moles are small — typically under 6mm (¼ inch), roughly the size of a pencil eraser or smaller. They tend to stay the same size over time.
A mole larger than a pencil eraser (6mm+), especially if it has been growing. However, melanomas can also be smaller when first detected — some start at just 3-4mm.
While melanomas are often larger than 6mm when diagnosed, they can be smaller. Any mole larger than a pencil eraser should be monitored carefully. However, don't ignore smaller moles that show other warning signs.
Melanomas can start small—some are detected at 3-4mm. Size is just one factor.
Evolution
Any change in size, shape, color, or symptoms over time
A mole that has looked the same for years — same size, same shape, same color. Stable moles are generally reassuring.
A mole that has recently changed: growing larger, developing new colors, changing shape, becoming raised when it was flat, or developing new symptoms like itching, bleeding, or crusting.
This may be the most important criterion. Any mole that changes—growing larger, changing shape or color, developing new symptoms like itching, bleeding, or crusting—requires professional evaluation.
Evolution is often the first sign of melanoma. Take monthly photos to track changes.
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Why one check is rarely enough
A single scan tells you about one spot, on one day. But skin changes are about patterns over time — a new mole appearing, a slow shift in shape, size or colour, or a patch that simply isn't healing. Monitoring the same spots side-by-side, week after week, surfaces the subtle changes a one-off check will always miss — and gives you a clear record to show a clinician if something needs a closer look.
(ScanSkinAI is a screening and monitoring tool, not a diagnosis. Always see a clinician for anything that is changing, bleeding, or worrying you.)
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Related reading: How to track moles over time · Changes in mole pictures
Beyond ABCDE: The Ugly Duckling Sign
In addition to the ABCDE rule, dermatologists use the "ugly duckling" sign — looking for moles that simply look different from all your other moles. Most people have a "signature" mole pattern; a mole that stands out as the "odd one" deserves attention.
This approach is particularly useful for people with many moles, where comparing each mole to ABCDE criteria would be impractical. If one mole looks distinctly different from your others, get it checked.
AI Mole Checking vs Dermatologist — When Do You Need Each?
An AI mole checker can screen moles using ABCDE criteria in seconds — great for regular monitoring and catching changes early. But it's a triage tool, not a diagnostic device.
If the AI flags concern, or if you notice any ABCDE warning signs yourself, see a dermatologist. Want to understand exactly what AI can and can't detect? We've written an honest guide.
When to seek medical help
The three tiers below are aligned with NICE NG12 (Suspected cancer: recognition and referral). If you are unsure which tier applies, default to the more urgent one.
Routine GP appointment
Book a routine appointment for a long-standing mole you have never had checked, general reassurance about your moles, or a mole that looks slightly different from your others (ugly duckling sign) but is not changing.
Prompt review (within 2 weeks)
Ask for a prompt appointment for a mole showing one or more ABCDE features, any mole that is changing in size, shape, or color, a mole that itches or becomes painful, or a new mole appearing after age 30.
Urgent — 2-week-wait referral
NICE NG12 recommends an urgent suspected-cancer (2-week-wait) referral for any pigmented lesion suspicious for melanoma — for example, a lesion scoring 3 or more on the weighted 7-point checklist, a mole that bleeds, a new pigmented streak under a nail, or a sore that doesn't heal within 3 weeks. Contact your GP, NHS 111, or the equivalent service in your country without delay.
Most moles that are checked turn out to be benign. The goal isn't to cause alarm — it's to catch the rare melanoma early when it's most treatable.
How to Perform a Monthly Self-Examination
Get good lighting
Use a well-lit room with a full-length mirror and a hand mirror for hard-to-see areas.
Check everywhere
Examine your entire body — including scalp, between toes, palms, and under nails. Ask a partner to help with your back.
Document with photos
Take clear photos of suspicious moles to track changes. Our AI mole checker can help document and analyze them.
Apply the ABCDE rule
Evaluate each mole against the five criteria. Also look for any 'ugly duckling' moles that stand out.
Who Should Be Extra Vigilant?
While everyone should perform regular skin checks, some people have higher melanoma risk:
- Fair skin, light hair, or light eyes
- History of sunburns, especially blistering sunburns
- Many moles (50+) or atypical/dysplastic moles
- Family history of melanoma or skin cancer
- Personal history of skin cancer
- Weakened immune system
- Regular tanning bed use or excessive sun exposure
If you have multiple risk factors, consider more frequent dermatologist visits (every 3–6 months) and diligent monthly self-examinations.
How AI Mole Checkers Compare
If you're looking for an AI tool to help with ABCDE screening, see our honest comparison of ScanSkinAI vs SkinVision — covering price, conditions detected, skin tone support, and accuracy.
Ready to check your moles?
Upload a photo to our free AI mole checker. It evaluates all five ABCDE criteria and 30+ conditions — instant results, no account needed.
Frequently Asked Questions
Frequently Asked Questions
The ABCDE rule is a widely used educational guide that helps people and clinicians spot moles that may need closer review for possible melanoma. It stands for Asymmetry, Border irregularity, Color variation, Diameter larger than 6mm, and Evolving changes. Any mole showing one or more of these features should be evaluated by a GP or dermatologist — it does not diagnose melanoma on its own.
While the ABCDE rule is highly effective, it may miss some melanomas—particularly nodular melanoma or amelanotic (non-pigmented) melanoma. That's why regular dermatologist check-ups remain important, especially if you have many moles or a family history of skin cancer.
Asymmetry means one half of the mole doesn't match the other half. If you drew a line through the center, the two sides would look different in shape, size, or color. Most benign moles are symmetrical—meaning both halves look roughly the same.
Concerning borders are ragged, notched, blurred, or have uneven edges that fade into surrounding skin. Normal moles typically have smooth, well-defined, even borders. If edges look like they're 'bleeding' into surrounding skin, get it checked.
Multiple colors within a single mole are concerning—especially combinations of brown, black, red, white, or blue. Normal moles are usually a single shade of brown. Melanomas often show uneven color distribution or unusual colors.
Traditionally, moles larger than 6mm (about pencil eraser size) were flagged. However, melanomas can be smaller—some are detected at 3-4mm. Size alone isn't diagnostic; it's one factor combined with other ABCDE criteria.
Watch for any evolution: changes in size, shape, color, elevation, or new symptoms like itching, bleeding, or crusting. The 'E' for Evolution may be the most important criterion—any changing mole warrants professional evaluation.
Perform monthly self-examinations at home and have a professional skin check annually (more frequently if you have risk factors). Use our AI mole checker to document and track changes between dermatologist visits.
AI mole checkers like ScanSkinAI can help screen moles using ABCDE criteria and flag those needing professional evaluation. Published studies of similar AI tools report clinical concordance with expert review broadly in line with general practitioners — they are a triage and monitoring aid, not a diagnostic device, and should complement rather than replace dermatologist care.
Don't panic, but do act. Schedule an appointment with a dermatologist within 1-2 weeks. Take clear photos of the mole to track any further changes. Most evaluated moles turn out to be benign, but early detection of melanoma significantly improves outcomes.
Related Mole & Melanoma Articles
ABCDE Rule: How to Use It at Home (worksheet)
At-home walkthrough with a printable self-rating worksheet.
AI Mole Checker vs Dermatologist
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What AI Mole Checkers Can & Can't Detect
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Melanoma vs Normal Mole
Side-by-side comparison of melanoma and benign moles.
When to Worry About a Mole
12 red flags that mean a mole needs medical attention.
Moles in Children: When to Worry
Parent's guide to normal childhood moles vs warning signs.
After a Mole Biopsy: What to Expect
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How to Check Your Skin for Skin Cancer
A simple step-by-step guide to a monthly skin self-check at home.