How to Check Your Moles: The ABCDE Rule and the Ugly Duckling Sign

Skin is the one organ you can examine yourself, which makes melanoma unusual among cancers: it is often visible long before it is dangerous. Found early, the five-year survival rate in the US is around 99 percent, and that number falls sharply once it has spread. A monthly self-check takes ten minutes and needs nothing but a mirror and decent light. Here is how to do it properly.

The ABCDE rule, letter by letter

This is the standard framework dermatologists teach, and it is worth memorising because it turns a vague sense that something looks off into something you can describe.

• A for Asymmetry: draw an imaginary line through the middle. If one half does not match the other, that is a flag. Ordinary moles are usually symmetrical.
• B for Border: edges that are irregular, ragged, notched or blurred rather than smooth and clearly defined.
• C for Colour: more than one colour in the same spot, or uneven shades of brown, tan, black, and sometimes red, white or blue.
• D for Diameter: larger than about 6 mm, roughly the width of a pencil eraser, though melanomas can be smaller when caught early.
• E for Evolving: any change over time in size, shape, colour or thickness, or new symptoms such as itching, bleeding or crusting.

Of the five, E does most of the work. A spot that is changing deserves attention regardless of how it scores on the other letters, and it is the reason a mental snapshot or an actual photograph is more useful than any single inspection.

The ugly duckling sign, which catches what ABCDE misses

ABCDE has a limitation: it judges each spot on its own. The ugly duckling approach works differently and is often better in practice. Most of your moles resemble each other, forming a family with a broadly similar look. A melanoma tends to stand out from that family, and your eye is surprisingly good at spotting an odd one out even when you cannot say why.

The line dermatologists use is worth remembering: not every ugly duckling is a melanoma, but most melanomas are ugly ducklings. So instead of examining each mole in isolation, scan a whole area and ask which one does not belong. Something noticeably darker, larger, redder, or simply different in character from its neighbours earns a closer look, even if it passes every ABCDE test.

How to actually do a self-exam

Do it monthly, in good light, after a shower when the skin is clean. Use a full-length mirror and a hand mirror, and enlist someone for the areas you cannot see. Working in the same order each time makes it easier to notice change.

Start with the face, ears, neck and scalp, parting the hair in sections or using a hairdryer on a cool setting. Move to the chest and torso, and for women, check under the breasts. Raise each arm and inspect the underarms, both sides of the arms, the palms, the backs of the hands, between the fingers and under the nails. Use the hand mirror for the back, the buttocks and the backs of the legs. Sit down for the front of the legs, then the tops and soles of the feet, between the toes and under the toenails. Photographs of anything you are unsure about, taken with something for scale, make the next check far more meaningful than memory alone.

The places people never look

Melanoma occurs in places that never see the sun, which surprises people and delays diagnosis. Check the soles of the feet, between the toes, under the nails on both hands and feet, the scalp, the ears, the genital area and the buttocks. Acral melanoma, which appears on palms, soles and under nails, is a well-recognised type, and it is disproportionately the type diagnosed late in people with darker skin.

That last point deserves emphasis. Skin cancer is less common in people with darker skin but is more often diagnosed at an advanced stage, partly because both patients and clinicians are less likely to be looking for it. A new dark streak under a nail that was not caused by an injury, a sore that does not heal, or a changing patch on the sole is worth showing to a doctor regardless of skin tone. The other cancers to watch for are basal and squamous cell carcinoma, which usually appear as a persistent scaly patch, a pearly bump or a sore that keeps bleeding and healing.

Who needs to be more vigilant

Risk is higher if you have fair skin that burns easily, red or blonde hair, many moles, a history of blistering sunburns, particularly in childhood, a family or personal history of skin cancer, a weakened immune system, or a history of sunbed use. Sunbeds are a particularly clear risk and are classified as carcinogenic.

If several of those apply to you, ask a doctor whether periodic professional skin checks make sense, since higher-risk people are often advised to have them. Total-body photography is offered in some clinics for people with very many moles, and it makes tracking change considerably easier. Meanwhile the prevention side has not changed: daily sunscreen, shade in the middle of the day, and covering up remain the most effective things you can do, and they matter more than any checking routine.

When to see a doctor

Book an appointment for any mole that is changing, any new spot that looks different from your others, a sore that has not healed within a few weeks, a mole that itches, bleeds or crusts, or a new dark streak under a fingernail or toenail. Do not wait for it to meet every ABCDE criterion, because early melanomas frequently do not.

It is far better to have a dermatologist tell you a spot is harmless than to watch it for another six months. Melanoma is one of the clearest examples in medicine where timing changes the outcome dramatically, and no clinician is irritated by someone bringing in a normal mole. This is general information rather than medical advice, and no article or phone app can diagnose a lesion. If something on your skin is bothering you enough to keep looking at it, that is reason enough to get it examined.

Frequently asked questions

What are the ABCDEs of melanoma?

Asymmetry, irregular Border, more than one Colour, Diameter larger than about 6 mm, and Evolving, meaning any change in size, shape, colour or symptoms such as itching or bleeding.

What is the ugly duckling sign?

The idea that most of your moles look similar to each other, so a melanoma tends to stand out as the odd one. Not every odd-looking mole is melanoma, but most melanomas look different from their neighbours.

How often should I check my skin?

Monthly is the usual recommendation, in good light with a full-length and hand mirror, following the same order each time so changes are easier to notice.

Can you get melanoma in places the sun never reaches?

Yes. Melanoma occurs on the soles, palms, under nails, on the scalp and in the genital area. These sites are often diagnosed late because people do not check them.

Should I use a mole-checking app?

Not as a substitute for a doctor. Apps can miss melanomas and provide false reassurance. If a spot concerns you enough to photograph it, it is worth having examined properly.

Read next

• Daily Sunscreen: The Single Best Anti-Aging Habit

  The prevention side of the same problem.

• Chemical vs Mineral Sunscreen: Which Should You Actually Use?

  Choosing the protection you will actually wear.

• How Skin Ages: What Is Genetics, What Is Lifestyle

  What sun exposure does to skin over decades.

This article is for general informational purposes only and is not medical advice. Always consult a qualified healthcare professional about your individual situation, and never start or stop a medication without your doctor. See our Medical Disclaimer.