Most moles on our bodies are completely harmless. The problem arises when a mole starts to change — and that is exactly where the ABCDE rule comes in. It is a simple method that lets anyone make a preliminary assessment of whether a mole needs a dermatologist's attention.
A Asymmetry
A healthy mole is usually symmetrical — if you divided it in half, both halves would look similar. If one half of a mole clearly differs from the other (in shape, colour, or thickness), that is a signal worth watching.
In J-Skin you can use the symmetry axis tool in the Analysis screen to overlay a dividing line on your mole photo and easily check whether both sides match.
B Border
Benign moles have smooth, well-defined borders. Borders that are concerning include:
- Irregular — jagged or wavy edges
- Blurred — the edge of the mole blends gradually into the surrounding skin
- Notched — deep indentations cutting into the mole
J-Skin uses an 8-sector border clock in the ABCDE module — you can mark which sectors have an abnormal border.
C Colour
A typical mole has a uniform colour — different shades of brown are normal, but they should be evenly distributed. Concerning signs include:
- Multiple clearly distinct colours (dark brown, light brown, black, red, white, blue)
- A sudden colour change in part of the mole
- The appearance of a new shade
The colour sampling tool in J-Skin lets you tap different spots on the mole photo and see how many colour shades are present.
D Diameter
The classic threshold is 6 mm — roughly the size of a pencil eraser. Moles larger than 6 mm should be watched carefully. However:
Many melanomas are smaller than 6 mm at the time of detection. Diameter is one criterion, not the only one.
J-Skin automatically measures moles in millimetres using coin calibration — simply place a coin next to the mole when taking a photo and the app will calculate the actual size.
E Evolution
This is the most important criterion. Any change in a mole's appearance — shape, colour, size, texture — or the appearance of new symptoms (itching, bleeding, crusting) is a reason to visit a dermatologist.
That is exactly why J-Skin was created: regularly photographing moles and comparing photos over time allows you to catch changes that are hard to notice with the naked eye.
When should you see a dermatologist immediately?
Do not wait for your next monitoring session if you notice:
- A mole that bleeds without any injury
- A mole that itches or hurts
- A new mole that is growing rapidly
- A mole that looks completely different from all the others on your body (the so-called ugly duckling sign)
- A dark streak under a fingernail or toenail
How does J-Skin help with the ABCDE rule?
The app offers a complete set of tools for each criterion:
- A — Symmetry axes and mirror reflection in the Analysis screen
- B — 8-sector border clock in the ABCDE module
- C — Colour sampling and posterisation in the Analysis screen
- D — Automatic measurement in mm with calibration using 7 coins
- E — Photo history, 4 comparison modes, diameter chart, timelapse
Frequently asked questions
What does each letter in the ABCDE rule mean?
A is asymmetry (the halves of the mole differ), B is border (uneven, jagged or blurred edges), C is color (several shades or uneven coloring), D is diameter (the classic threshold is over 6 mm), and E is evolution, meaning change over time. It is a simple observation aid, not a diagnosis.
Can a mole smaller than 6 mm be dangerous?
Yes. The 6 mm threshold is only a guideline, not a strict cutoff. Melanoma is sometimes found in smaller lesions, especially when they change quickly, look asymmetric or have uneven color. Show any suspicious mole to a dermatologist regardless of its size.
Is the ABCDE rule enough to rule out melanoma?
No. ABCDE helps you spot warning signs, but it is not a diagnostic test and does not catch every case. Some melanomas do not meet these criteria. J-Skin is an educational app that supports observation, not a medical device. A diagnosis always belongs to a doctor.
This article is educational, written by the J-Skin team based on the reputable, publicly available sources listed below. It is not medical advice or a diagnosis and does not replace a consultation with a dermatologist.
Sources
Start monitoring your moles
Download J-Skin for free and check your moles with the ABCDE rule.
Get it on Google Play