How to tell if a mole is dangerous

The ABCDE rule

It is the most useful screening tool there is, and you can use it yourself in five minutes in front of a mirror:

• A — Asymmetry. Draw an imaginary line through the middle. A benign mole usually has two similar halves. If one half does not match the other, note it.
• B — Border. Benign moles have smooth, defined edges. Irregular, notched, blurred or “bleeding-out” borders into the surrounding skin are a warning sign.
• C — Colour. A benign mole is usually one shade. What concerns is several colours within the same lesion — different browns, black, red, white or blue.
• D — Diameter. Classically, larger than 6 mm (a pencil eraser). But careful: a melanoma can be smaller, so size never rules anything out on its own.
• E — Evolving. The most important of the five. Any change over time: size, shape, colour, elevation; starting to itch, hurt or bleed; a crust that will not heal. A mole unchanged for twenty years is far less worrying than one that has changed in three months.

The “ugly duckling” sign

A simple and surprisingly powerful clinical trick: a person’s moles tend to resemble one another. They usually share a family look.

So when one looks clearly different from all the others — darker, larger, a different shape, a different elevation — that is the one to show. It does not need to satisfy the full ABCDE. It only needs to stand out.

Do not wait: seek care immediately if…

Some signs are not for “watching a few weeks”:

• A mole that bleeds without being knocked or scratched.
• A lesion that will not heal: a crust or sore that has not closed for weeks.
• A mole that grows quickly or becomes raised and firm.
• A dark longitudinal band in a nail, especially if new, widening, or staining the skin around the nail. See nail fungus: this is not a fungus until someone proves it.
• Any new lesion in an adult that grows and resembles nothing else of yours.

⚠️ What must NEVER be done with a mole

This is probably the most important part of this guide.

A mole is never burned, frozen or cut off without being studied first. Not with laser, not with nitrogen, not with “a product”, and not in a beauty salon.

The reason is devastating: if that lesion was a melanoma, destroying it destroys the evidence. The chance to measure its depth is lost — and depth is exactly what determines prognosis and treatment — and the patient goes home believing it was “removed”, while the disease may keep advancing underneath.

The correct approach is always the same: excise it completely and send it to pathology. Always. Without exception. See mole and wart removal.

Who should check, and how often

Monthly self-examination in front of a mirror is free and finds most cases: use ABCDE, get help for your back and scalp, and do not forget soles, palms and nails — where, on darker skin, melanoma appears more often and is found later.

A medical check with dermoscopy is what sees what the eye cannot. It matters especially if you have many moles, a family history of melanoma, blistering sunburns in childhood, or very fair skin. See skin cancer screening.

And a note that matters in Mexico: darker skin also develops melanoma, frequently in sun-protected sites — soles, palms, nails — and precisely for that reason it tends to be diagnosed later and at a worse stage. Not tanning or burning does not mean you should not be checked.

Frequently asked questions

Every figure published on this site is approximate and is not a quote. Any procedure or treatment first requires a private assessment consultation with Dr. Arístides Arellano —$800 MXN, charged separately— and it is at that consultation that the definitive cost of your case is determined.

Educational content; it does not replace a medical consultation. Results may vary from person to person.