Moles: How to Tell a Normal One From One That Needs Checking
Most moles are entirely harmless, and most people have between ten and forty of them. The purpose of knowing what to look for is not to worry about every spot, but to recognise the small number that behave differently.
The ABCDE rule
A practical checklist for pigmented lesions.
A for Asymmetry. One half does not match the other.
B for Border. Edges that are irregular, scalloped, notched or blurred rather than smooth and well-defined.
C for Colour. More than one colour within the lesion: shades of brown, black, and sometimes red, white or blue. Uniform colour is reassuring.
D for Diameter. Larger than about 6 mm, roughly the width of a pencil eraser. This is the weakest criterion, because melanomas can be smaller and many harmless moles are larger.
E for Evolving. Changing in size, shape, colour, or elevation, or developing new symptoms such as itching, bleeding or crusting.
E is the most important letter. A lesion that is changing deserves assessment even if it satisfies none of the other criteria.
The ugly duckling sign
Most of a person’s moles resemble each other, like siblings. A lesion that looks clearly different from all your others, in colour, shape or size, is the ugly duckling, and it deserves a look regardless of whether it fits ABCDE.
This sign is often more useful in practice than the checklist, because it relies on comparison rather than absolute measurement.
What melanoma looks like on darker skin
This is where delays happen, and the delay is costly.
Melanoma is less common in people with darker skin, but it is diagnosed at a later stage and has worse outcomes. One reason is that the common type in darker skin is acral lentiginous melanoma, which appears in places people do not think to check and which are not sun-exposed:
- Palms of the hands
- Soles of the feet
- Under the fingernails or toenails
- Mucous membranes, including inside the mouth
A nail sign to know: a dark streak running the length of a nail, particularly a single nail, that is widening, is darker than other streaks, is irregular, or where pigment extends onto the surrounding skin fold. That last feature, called Hutchinson sign, is particularly concerning. Multiple uniform streaks across several nails are common and usually benign in people with darker skin.
A dark spot on the sole that is growing is not a bruise to wait out.
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Other skin cancers
Basal cell carcinoma, the most common skin cancer. A pearly or waxy bump, often with visible tiny blood vessels, that may bleed, crust and never fully heal. Slow growing, rarely spreads, but destroys local tissue if left.
Squamous cell carcinoma. A firm red nodule, or a scaly crusted patch, sometimes tender, often on sun-exposed areas. Can spread if neglected.
Actinic keratosis. Rough, scaly patches on sun-damaged skin. Precancerous and treatable.
The common theme: a sore that does not heal within a month, or a lesion that bleeds repeatedly without being injured, deserves examination.
Who is at higher risk
- Fair skin that burns easily, light eyes, red or blond hair
- Many moles, particularly more than fifty
- Atypical or dysplastic moles
- A history of blistering sunburn, especially in childhood
- Use of tanning beds, which substantially increases risk and more so with younger age at first use
- Family history of melanoma
- Personal history of any skin cancer
- Immunosuppression, including after organ transplant
- Significant cumulative outdoor sun exposure
Self-examination
Every one to three months, in good light, with a mirror and ideally a partner’s help.
Cover: face, ears, scalp by parting the hair, neck, chest, torso, both sides of arms and hands, between fingers, nails, back and buttocks using a mirror, legs front and back, soles of feet, between toes, and the genital area.
Photographs are more reliable than memory. Taking dated photographs of your moles, with a ruler or coin for scale, makes change far easier to detect, since gradual change is almost impossible to recall accurately.
Sun protection, specifically
- Broad-spectrum sunscreen SPF 30 or higher, applied generously, which means roughly a teaspoon for the face and neck and about 30 mL for the whole body
- Reapply every two hours, and after swimming or heavy sweating
- Most people apply roughly a quarter to a half of the tested amount, which means an SPF 50 behaves like a much lower number
- Shade between about 10 am and 4 pm
- Clothing, a wide-brimmed hat and sunglasses, which outperform sunscreen
- No tanning beds
- Sunscreen daily on the face year-round in high-UV regions
People with darker skin still need sun protection, both for skin cancer and for pigmentation, though the melanomas most common in darker skin are largely not sun-related, which is why checking palms, soles and nails matters independently of sun habits.
When to see a doctor
- Any mole that is changing
- A lesion that looks different from your others
- A sore that has not healed in a month
- A new lesion appearing after about 40
- A dark streak in a nail, particularly a single widening one
- Any pigmented spot on a palm or sole
- A mole that itches, bleeds or is painful
Dermoscopy, a magnified lit examination, substantially improves accuracy over the naked eye, and excision with histology remains the definitive answer.
The short version
Change is the most important sign, and the lesion that stands out from all your others deserves attention even if it looks ordinary. If you have darker skin, check palms, soles and nails specifically, because that is where melanoma hides and where it is found late. And nothing that bleeds repeatedly or fails to heal in a month should be left alone.