What you can do about the scary truth behind the ABCDEs of melanoma

July 18, 2026 · William S. Farmer, MD

If you’ve read anything about checking your skin, you’ve seen the ABCDEs: Asymmetry, Border irregularity, Color variation, Diameter over 6mm, Evolving. It’s a genuinely useful checklist – and it’s also incomplete. That’s not a reason to be discouraged by it. It’s the reason a specialist exists: to fill in exactly the gaps a five-letter mnemonic can’t cover on its own. None of this is a tool for diagnosing yourself. It’s a guide for knowing which spots are worth mentioning at your next visit, which are worth making an appointment over sooner, and which are fine to simply keep an eye on – and getting that sorted out is a genuinely easy, worthwhile thing to do. (If you are wondering how often that should happen, we cover that separately in how often you should really get a skin check.)

The ABCDEs, quickly

The original ABCD criteria were developed in the 1980s to help both patients and physicians spot concerning pigmented lesions without special equipment. [1] Later research added the fifth letter:

• Asymmetry – one half doesn’t match the other.
• Border – edges that are irregular, notched, or blurred rather than smooth.
• Color – more than one shade, or colors that don’t look like the person’s other moles.
• Diameter – larger than about 6mm (roughly a pencil eraser), though melanoma can be smaller.
• Evolving – any change in size, shape, color, or symptoms (itching, bleeding) over time. [1]

This checklist works well because it was built around the most common type of melanoma – superficial spreading melanoma – which typically grows outward along the skin’s surface before it grows deep, producing exactly this kind of irregular, slowly changing spot. That growth pattern gives ABCDE time to catch it.

It’s worth being clear about what ABCDE is actually for, because this is the single most misunderstood part of it. It’s not a threshold for deciding what needs to come off. Some people naturally have moles larger than 6mm, or moles with more than one shade of brown, for their entire lives without any problem at all – and other people’s moles simply run large or multi-toned as a personal pattern, not a warning sign. Checking a box on this list doesn’t mean “biopsy this.” It means “mention this.” What actually needs a biopsy, a photo to track, or nothing at all is exactly the judgment call a specialist is there to make – ABCDE’s whole job is telling you what’s worth putting in front of one. If you see something that fits any of these, say something. That’s the entire ask.

Nodular melanoma: symmetric, uniform, and growing fast

Nodular melanoma behaves differently: instead of spreading outward first, it grows downward from the start. [2] The result is a lesion that’s often symmetric, a single color rather than variegated, and smaller than 6mm for much of its course – it can fail every letter of ABCDE at once, right up until it’s already deep. [2] What it does have is what the ABCDE checklist doesn’t ask about: it’s usually raised, firm to the touch, and visibly growing week to week. Researchers have proposed a separate checklist for exactly this pattern – Elevated, Firm, and Growing – to catch what ABCDE is structurally unable to. [2] The takeaway isn’t to worry about every bump; it’s that a spot simply getting bigger week over week belongs on your specialist’s radar, whatever it looks like – not something to watch and decide about on your own.

Amelanotic melanoma: when there’s no color at all

The other major blind spot is color itself – or the lack of it. Amelanotic melanoma produces little or no pigment, so it can look pink, red, or skin-colored rather than dark, and it’s been described in the medical literature as “the great masquerader” because it can resemble a pimple, a scar, a wart, or a harmless bump rather than anything that looks like a mole. [3] “Color variation” simply isn’t a useful question to ask about a lesion that has no color to vary – so the practical version of this is simple: something new or changing is worth flagging for your dermatologist, even when it doesn’t look pigmented at all. You don’t have to know what it is to bring it up.

New moles after 40 deserve a second look

Here’s a detail most people don’t know, and it’s a genuinely useful one: most people’s mole-forming years wind down by their mid-30s to 40s. One large twin study found that nevus density rises steadily until around age 35, then gradually declines from there. [5] So a mole that shows up for the first time well into adulthood is a somewhat different event than one that showed up at 16 – it’s simply less common, which is part of why researchers who study nevi directly describe new mole growth in older adults as uncommon and worth paying attention to. [6]

This connects to something else worth knowing: most melanomas don’t come from an existing mole at all. In a pooled analysis of nearly 40 studies, about 71% of melanomas arose fresh (de novo) rather than from a pre-existing nevus. [7] So the useful habit isn’t just watching your existing moles for change – it’s noticing brand-new spots, period, especially later in life. A new spot appearing at 45 isn’t a reason to panic – it’s simply a reason to say something at your next visit, or sooner if anything else about it stands out. Noticing it is your job; deciding what it is isn’t.

Palms, soles, and nails are not the same as everywhere else

Acral lentiginous melanoma – the subtype that shows up on the palms, soles, and in or around the nails – deserves its own mention, for two reasons. First, it doesn’t follow the same visual patterns as melanoma elsewhere on the body, so it’s genuinely easy to miss or mistake for something else. Second, it disproportionately affects people of Asian and African descent, populations for whom melanoma is overall much less common – which means both patients and clinicians can be slower to consider it. [8] In one study from Singapore, acral melanoma was the single most common subtype in Asian patients, and it took more than twice as long to diagnose as other subtypes. [9]

Because of that combination – easy to miss, and often diagnosed late when it is finally caught – this is one spot on the body where the right move is simple and immediate, not “watch and see”: any new or changing spot on the palms, soles, or in or around a nail should be photographed right away, followed by an appointment with a specialist. While you’re waiting for that appointment, keep photographing it weekly so you and your specialist can see exactly how it’s changed by the time you’re seen. This is the one place on this list where “say something soon” isn’t a suggestion – it’s the whole point.

The “ugly duckling” sign

If ABCDE describes what to look for in a single spot, the “ugly duckling” sign describes a faster way to scan an entire body of moles. Most people’s moles share a family resemblance – similar size, shape, and color as each other, like siblings. The idea is simple: a mole that doesn’t match that pattern, that looks different from everything else on your skin, is worth having looked at, regardless of whether it happens to check any of the ABCDE boxes on its own. [4] It’s a comparison-based heuristic rather than a checklist – and it catches exactly the cases above, since a nodular, amelanotic, or acral melanoma will often still stand out as the “different one,” even when it fails every individual ABCDE criterion. You don’t need to explain why a spot looks off to bring it up – “it just looks different from my others” is a complete, useful reason to mention something. (This one has its own article, covering how to use it and the situations where it does not work.)

The bottom line

None of this – not ABCDE, not EFG, not the ugly duckling sign, not any of it – is meant to turn you into your own diagnostician. That was never the point, and it’s worth repeating one more time: nothing here is a reason to biopsy something yourself or to decide it’s nothing on your own, either. It’s a way of noticing. The deciding is what a specialist is for. Say something about what you notice, and let that appointment do the rest. Most of the time, it ends with good news and a plan for when to check again – and that peace of mind, on its own, is worth the trip.

References

1. Abbasi NR, Shaw HM, Rigel DS, et al. Early diagnosis of cutaneous melanoma: revisiting the ABCD criteria. JAMA. 2004;292(22):2771-2776. doi:10.1001/jama.292.22.2771
2. Kelly JW, Chamberlain AJ, Staples MP, McAvoy B. Nodular melanoma. No longer as simple as ABC. Aust Fam Physician. 2003;32(9):706-709.
3. Koch SE, Lange JR. Amelanotic melanoma: the great masquerader. J Am Acad Dermatol. 2000;42(5 Pt 1):731-734. doi:10.1067/mjd.2000.103981
4. Grob JJ, Bonerandi JJ. The ‘ugly duckling’ sign: identification of the common characteristics of nevi in an individual as a basis for melanoma screening. Arch Dermatol. 1998;134(1):103-104. doi:10.1001/archderm.134.1.103-a
5. Falchi M, Spector TD, Perks U, Kato BS, Bataille V. Genome-wide search for nevus density shows linkage to two melanoma loci on chromosome 9 and identifies a new QTL on 5q31 in an adult twin cohort. Hum Mol Genet. 2006;15(20):2975-2979. doi:10.1093/hmg/ddl227
6. Cabral ES, Chen FW, Egbert BM, Swetter SM. Acquired blue nevi in older individuals: retrospective case series from a Veterans Affairs population, 1991 to 2013. JAMA Dermatol. 2014;150(8):873-876. doi:10.1001/jamadermatol.2013.7366
7. Pampena R, Kyrgidis A, Lallas A, Moscarella E, Argenziano G, Longo C. A meta-analysis of nevus-associated melanoma: Prevalence and practical implications. J Am Acad Dermatol. 2017;77(5):938-945.e4. doi:10.1016/j.jaad.2017.06.149
8. Stubblefield J, Kelly B. Melanoma in non-Caucasian populations. Surg Clin North Am. 2014;94(5):1115-1126. doi:10.1016/j.suc.2014.07.008
9. Lee HY, Chay WY, Tang MB, Chio MT, Tan SH. Melanoma: differences between Asian and Caucasian patients. Ann Acad Med Singap. 2012;41(1):17-20.

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Medical content: William S. Farmer, MD · Last reviewed: July 2026