Mole checks and the ABCDE rule: how to tell whether a mole could be dangerous

What exactly is a mole?

A mole, medically known as a melanocytic nevus, is a generally benign proliferation of melanocytes — the cells involved in melanin production. Moles can be flat or raised, light or dark, round or oval, small or relatively large. Some are present from birth, while others appear later in life.

Therefore, a dark mole is not automatically dangerous, and a raised mole does not mean melanoma either. What matters most is its pattern and, above all, how it changes over time.

How can you tell if a mole is dangerous?

We cannot confirm whether a mole is benign or malignant simply by looking at it at home. However, there are warning signs that should prompt a medical evaluation. One of the most well-known tools is the ABCDE rule.

ABCDE stands for: A — Asymmetry, B — Border, C — Color, D — Diameter, and E — Evolution. It is a simple rule that helps identify some common characteristics of melanoma.

What does the A for Asymmetry mean?

Imagine dividing a mole in half. In a typical benign nevus, both halves tend to look relatively similar. In a suspicious lesion, one half may not resemble the other — that is asymmetry.

However, we must be careful. Not every slightly asymmetrical mole is a melanoma. There are atypical benign nevi that can show some degree of asymmetry. The ABCDE rule identifies warning signs; it does not establish a diagnosis.

What does the B for Border mean?

Benign moles tend to have relatively regular, well-defined, and uniform borders. In certain suspicious lesions, we may find irregular, jagged, poorly defined, or scalloped borders that become progressively difficult to distinguish from the surrounding skin.

That is why the B stands for irregular borders. Border irregularity is a sign that should be assessed alongside the other characteristics of the lesion.

What does the C for Color mean?

A benign mole can be light brown, dark brown, almost black, pinkish, or skin-colored. What matters is not simply that it is dark. We are particularly concerned about a lesion in which different colors are distributed unevenly: light brown, dark brown, black, reddish, white, or bluish.

That is why the C stands for non-uniform color. A lesion with multiple colors does not automatically mean melanoma, but it does deserve careful evaluation.

What does the D for Diameter mean?

Traditionally, 6 millimetres is used as a reference — roughly the size of a pencil eraser. That is why D stands for diameter.

But there is a very common mistake here. A melanoma can measure less than 6 mm. The ABCDE rule itself acknowledges that, although many melanomas are larger than 6 mm at the time of diagnosis, some are smaller. Therefore, saying 'it is only 4 mm, so it cannot be a melanoma' is incorrect: diameter is one clue among many, not a guarantee of benignity.

What does the E in evolution mean?

It is probably one of the most important letters. E stands for evolution — that is, change. A mole that was stable and begins to grow, change shape, change colour, become raised, bleed, itch, form a crust, or simply behave differently deserves to be evaluated.

Leading medical organisations consider a new or changing lesion to be one of the most important warning signs of melanoma. That is why I would add a very simple phrase: a mole that changes deserves a closer look.

What is the 'ugly duckling' sign?

It is one of the most interesting clinical tools for self-examination of moles. Each person tends to develop a certain pattern of moles: they may be small and light, large and dark, round or raised, but there is usually a degree of similarity among many of them.

Then a lesion appears that does not look like the others: that is the ugly duckling. The ugly duckling sign describes precisely a lesion that stands out because it has a different appearance from that person's usual mole pattern. It is a recognised sign for helping to detect lesions that warrant evaluation.

Why can the 'ugly duckling' sign be even more useful than memorising ABCDE?

Because people are not dermatology textbooks. Someone may have twenty large, slightly irregular moles that remain stable for years. Another person may have fifty small, perfectly uniform brown moles.

In this second person, a black, asymmetric mole suddenly appears that looks completely different. That mole immediately catches the eye — not because there is a universal standard for a 'normal mole', but because it is different from that person's other moles.

Does a melanoma always meet the ABCDE criteria?

No, and this is fundamental. ABCDE is an educational tool, not a perfect diagnostic test. Some melanomas can be small, relatively symmetrical, uniform in colour, or even poorly pigmented. Amelanotic melanomas exist, which can be pink or reddish and contain very little visible pigment.

That is why we must add other concepts to ABCDE: a new lesion, a different lesion, a lesion that changes, a lesion that bleeds without explanation, or a wound that does not heal. Suspicious lesions do not always look like the classic photographs of melanoma.

Do all melanomas arise from an existing mole?

No. This is another important myth. A melanoma can arise from a pre-existing melanocytic lesion or as a completely new lesion. That is why when a person says 'that mole was not there before', they are providing us with important information.

Especially when a new pigmented lesion appears in adulthood and also grows, changes, or behaves differently.

If a mole has hair, does that mean it is benign?

We cannot use that as a guarantee. A mole with hair can be perfectly benign, and this is very common. However, the presence of hair does not constitute proof of benignity.

The evaluation must be based on the history, the evolution, the clinical examination, and dermatoscopy when indicated — not on a single popular sign.

If a mole itches, does that mean it is melanoma?

Not necessarily. A mole can itch because it has been rubbed, is irritated, there is a dermatitis around it, or it has sustained a trauma. And many melanomas do not itch at all.

However, a mole that begins to cause persistent itching, pain, bleeding, ulceration, or any new symptom deserves an evaluation, especially if it is also changing.

If a mole bleeds, should I be concerned?

A mole can bleed because we have scratched it, cut it while shaving, or injured it. However, a lesion that bleeds spontaneously, ulcerates repeatedly, or forms a crust that keeps coming back should be examined.

Not only because it could be a melanoma. There are also other skin cancers, such as basal cell carcinoma or squamous cell carcinoma, that can present as lesions that bleed or wounds that do not heal. For this reason, skin cancer does not mean only melanoma.

How do you perform a correct self-examination of moles?

Self-examination of moles does not consist of quickly glancing at your arms: we must observe all the skin. A thorough self-examination can be performed in a well-lit room using a large mirror, a hand mirror, and, if possible, the help of another person for hard-to-see areas.

The American Cancer Society describes a systematic head-to-toe check and notes that many professionals advise performing it approximately once a month, although the frequency should be adapted to individual risk.

Which areas should we check?

We start with the face, nose, lips, ears, and neck. Then the chest, abdomen, arms, forearms, and hands, not forgetting the palms, the spaces between the fingers, and around and under the nails where possible.

We continue with the thighs, knees, legs, ankles, and feet, including the soles, the spaces between the toes, and the toenails. Using a mirror, we check the back, the back of the arms, the buttocks, the back of the legs, and the genital area. And finally the scalp, parting the hair with a comb or asking another person for help.

Why should we also look at the soles, nails, and areas that never receive sun?

Because melanoma does not appear exclusively where the sun shines. Ultraviolet radiation is one of the most important risk factors for many melanomas, but there are subtypes that can appear in areas with little sun exposure, such as the palms, the soles, or beneath the nails.

This is especially important to remember because melanoma can develop in any skin tone. In darker skin tones, certain melanomas can appear precisely in acral locations, which is why examining the palms, soles, and nails remains important.

How do you check a mole on a nail?

A pigmented band on a nail is called melanonychia. The majority are not melanomas and can have numerous benign causes. However, a new band — especially on a single finger in an adult — that widens, changes, shows irregular colors, causes nail abnormalities, or extends pigment onto the periungual skin requires evaluation.

The conventional ABCDE rule does not work in exactly the same way on nails. That is why a pigmented nail lesion requires its own dedicated assessment.

Should I take photographs of my moles?

It can be very useful, especially when a person has many moles. A photograph allows you to compare how things look today versus how they looked months ago, and change over time is precisely one of the criteria that interests us most.

In high-risk patients, European guidelines also contemplate professional tools such as total body photography and sequential digital dermatoscopy to improve the detection of early melanomas.

Can a mobile phone app tell me whether a mole is melanoma?

It should not replace a medical evaluation. There are apps and artificial intelligence systems capable of analyzing images of skin lesions, and it is a very interesting technological field. However, there are still issues related to accuracy, image quality, diversity of skin phototypes, lesion type, false positives, and — especially — false negatives.

The American Cancer Society notes that, although these tools continue to improve, concerns about their accuracy remain, and they should not replace the professional evaluation of a worrying lesion. An app that says 'low risk' should not reassure us if a lesion is clearly changing.

What does the doctor do during a mole check?

First, look. But looking medically means analyzing the distribution, pattern, symmetry, borders, color, evolution, and comparison with the rest of the lesions. Then we can use a fundamental tool: the dermatoscope.

What is dermatoscopy?

It is a non-invasive technique that allows us to observe structures within a skin lesion that cannot be adequately assessed with the naked eye. Using magnification and a lighting system, we can study pigmentary patterns, vascular structures, symmetry, color distribution, and other diagnostic characteristics.

Current European guidelines indicate that when melanoma is suspected, clinical evaluation should be complemented by dermoscopy. But we must remember that the dermoscope does not diagnose on its own: it is a tool that requires medical interpretation.

What is digital dermoscopy?

It allows dermoscopic images of certain lesions to be saved. We can then compare them with photographs taken months later, thereby detecting very subtle changes.

This can be especially useful in people with many nevi, atypical nevi, a personal history of melanoma, or high risk. European guidelines recognise the usefulness of sequential digital dermoscopy and total body photography in high-risk patients.

What is a 'mole map'?

We commonly refer to mole maps as systematic photographic monitoring strategies of the skin surface. Standardised images of the body are taken and, where appropriate, dermoscopic photographs of selected lesions.

The aim is not only to ask 'does this mole look unusual today?' but also 'has this mole changed since the last check-up?' This adds time to our evaluation, and in medicine, time can provide extraordinarily valuable information.

Does a total body photography system diagnose melanoma?

Total body photography and digital dermoscopy systems can help document lesions, compare them, identify changes and organise follow-up appointments, and systems with support algorithms can provide additional information. But no percentage generated by a machine should be interpreted as a histological diagnosis.

The clinical decision must integrate the history, examination, dermoscopy, evolution and, when a lesion is suspicious, biopsy or excision for histopathological study. European guidelines are clear: when melanoma is suspected, definitive confirmation requires histopathology.

If a mole looks suspicious, does it need to be removed?

If, after clinical and dermoscopic evaluation, there is sufficient suspicion of melanoma, we will usually need a histological study, which involves obtaining tissue. For a lesion suspected of being melanoma, the standard strategy is to perform a complete excision of the lesion with a narrow clinical margin, whenever technically possible, so that pathology can evaluate it correctly.

We must not destroy a suspicious pigmented lesion using laser, electrocoagulation or cosmetic procedures without first establishing what it is. Because if we destroy the tissue, we lose the ability to study it properly.

Should all moles be removed preventively?

No. Having many moles does not mean we should remove them all. The vast majority are benign, and systematically excising all nevi is not a reasonable melanoma prevention strategy.

What matters is identifying suspicious lesions, lesions that change, ugly ducklings and people with high risk.

Who is at greater risk of melanoma?

Among the known risk factors are fair skin, a tendency to burn, blond or red hair, numerous moles, atypical nevi, a personal history of melanoma, a significant family history, exposure to ultraviolet radiation, sunburns — especially severe ones — and immunosuppression.

The risk of melanoma is higher in fair-skinned individuals, although no skin phototype is completely protected.

Do childhood sunburns matter decades later?

Yes. The skin has biological memory. Ultraviolet radiation can cause DNA damage. A sunburn disappears visually within days, but that does not mean all the molecular damage has disappeared.

That is why skin cancer prevention begins in childhood.

Are tanning booths safer than the sun?

No. Tanning booths expose the skin to ultraviolet radiation, and there is no such thing as a 'healthy UV tan'. The American Academy of Dermatology recommends avoiding tanning beds and considers UV exposure the leading preventable risk factor for skin cancers, including melanoma.

Does sunscreen prevent all melanomas?

We cannot say 'I apply SPF 50, therefore I cannot get melanoma'. Photoprotection is a comprehensive strategy that includes avoiding excessive sun exposure, seeking shade, wearing clothing, a hat and sunglasses, applying an appropriate sunscreen, and avoiding tanning booths.

Sunscreen is not a licence to stay in the sun indefinitely: it is part of a strategy to reduce ultraviolet exposure.

How often should I have my moles checked?

Here we must avoid a one-size-fits-all recommendation. There is no single interval that is right for everyone. A person with few moles, no personal or family history, no atypical lesions and a low risk profile does not necessarily need the same follow-up as a person with hundreds of nevi, atypical nevi, a history of melanoma, a strong family history or immunosuppression.

The frequency of professional check-ups should be individualised according to risk. European guidelines recommend structured follow-up for patients with melanoma and recognise specific surveillance tools for high-risk individuals. For self-examination, many experts use approximately monthly checks as a reference — especially when there is increased risk — but we should not turn self-examination into a constant source of anxiety.

When should I seek attention without waiting for my next scheduled check-up?

If you notice a new mole that is growing, a clear change in size, shape or colour, a lesion that looks different from all the others, spontaneous bleeding, ulceration, a wound that does not heal, a rapidly evolving lesion, or a suspicious new pigmented band under a nail, do not simply wait to 'see how it looks next year': request an evaluation.

Why is detecting a melanoma early so important?

Because melanoma changes enormously depending on when it is diagnosed. When it is localised in the skin and detected early, treatment can be essentially surgical and the chances of control are very high. When it progresses and reaches the lymph nodes or other organs, the disease takes on a different dimension and may require systemic treatments.

That is why early detection is not a minor detail: it is a fundamental part of melanoma treatment. Current European guidelines place particular emphasis on early detection, dermatoscopic diagnosis, and histopathological confirmation.

What do I want you to remember about the ABCDE rule?

I don't want you to finish reading this article and start looking at every mole thinking 'could this be cancer?' I want exactly the opposite: for you to know your own skin. Learn what your pattern looks like — your usual moles, your freckles, your spots — and it will then be much easier to spot something that doesn't fit that pattern.

Remember: A for asymmetry, B for irregular borders, C for non-uniform colour, D for diameter — especially when it is increasing — and E for evolution. And add a sixth idea that needs no letter: the ugly duckling, that mole that looks like none of the others.