Skin Cancer: How Doctors Assess a Changing Mole

You noticed a mole that looks different. Maybe it grew, changed color, or started to itch. Or a partner pointed out a spot on your back that you cannot see. It is easy to worry. Most moles are harmless, but a changing mole deserves a look. This guide explains what doctors check and what happens next.

Moles and skin cancer

A mole (nevus) is a cluster of pigment cells called melanocytes. Most adults have between 10 and 40 common moles. Most never become cancer. [1]

There are three main types of skin cancer: [5]

• Basal cell carcinoma: the most common type. It grows slowly and rarely spreads, but it can damage nearby tissue.
• Squamous cell carcinoma: also common. It can spread if not treated.
• Melanoma: less common, but more likely to spread to other parts of the body. It can start in an existing mole or as a new spot.

Who has higher risk

Risk is higher for people with: [1] [5]

• Many moles, or large or unusual moles (dysplastic nevi).
• Fair skin that burns easily, light eyes, or red or blond hair.
• A history of sunburns, or use of tanning beds.
• A personal or family history of melanoma.
• A weak immune system, for example after an organ transplant.

What your doctor looks at

The ABCDE signs

Doctors use a simple checklist for melanoma. A spot with one or more of these features needs a closer look. [2]

• A for asymmetry: one half does not match the other.
• B for border: the edges are ragged, notched, or blurred.
• C for color: uneven color, with shades of brown, black, red, white, or blue.
• D for diameter: larger than about 6 mm, the size of a pencil eraser. Some melanomas are smaller.
• E for evolving: the mole changes in size, shape, color, or height, or starts to bleed, itch, or crust.

Experts added E because change over time is one of the most important warning signs. [2]

The ugly duckling sign

Most of your moles tend to look alike. A mole that looks different from all the others is called an ugly duckling. Doctors pay close attention to these spots, even if they do not meet the ABCDE signs.

The exam

• Your clinician asks when you first noticed the spot and how it has changed.
• They check the whole skin, not only the spot that worries you.
• Many use a dermatoscope, a handheld lens with a light that shows patterns under the skin surface.
• Some take photos to compare at a later visit.

Biopsy

A biopsy is the only way to know for sure if a spot is cancer. The doctor numbs the skin and removes all or part of the spot. A pathologist then looks at it under a microscope. [4]

For a spot that might be melanoma, doctors usually try to remove the whole spot with a small margin of normal skin. This gives the pathologist the full depth, which is key for staging. [4]

If it is melanoma

The pathology report gives the thickness of the tumor, measured in millimeters. This is called Breslow thickness. It also notes whether the surface is broken (ulceration). These features help set the stage and guide next steps, such as a wider excision or a lymph node biopsy. [4]

Found early, most melanomas can be cured with surgery. [4]

What screening guidance says

Screening means checking skin in people who have no symptoms or worrying spots.

• In the US, the US Preventive Services Task Force says there is not enough evidence to judge whether routine skin exams by a clinician help adults without symptoms. This is an "I" statement. It does not apply to people with a changing mole or a history of skin cancer. [3]
• In Canada, there is no national recommendation for or against routine skin cancer screening in people without symptoms. Dermatology groups encourage people to know their own skin.

Both countries agree: a new or changing spot is not a screening question. It should be checked.

Lowering your risk

Sun protection lowers the risk of skin cancer. [5]

• Seek shade, especially in the middle of the day.
• Wear clothing, a hat, and sunglasses.
• Use a broad-spectrum sunscreen with SPF 30 or higher on skin that is not covered.
• Avoid tanning beds.

Questions to ask your clinician

• Does this spot have any of the ABCDE features?
• Do you recommend a biopsy, and what kind?
• Should I see a dermatologist?
• How should I check my skin at home, and how often?
• Am I at higher risk because of my skin type or history?
• Would photos help track my moles over time?
• If it is cancer, what are the next steps?

When to get care quickly

Skin changes are rarely an emergency. Book a visit soon, within days to a few weeks, if a spot:

• Is new and growing quickly.
• Bleeds, oozes, or forms a sore that does not heal within a few weeks.
• Changes color or shape over weeks or months.
• Is a dark streak under a nail that is new or getting wider.

Bottom line

Most moles are harmless. A mole that is new, changing, or looks different from your others needs a check. Doctors use the ABCDE signs, the ugly duckling sign, and a dermatoscope to decide whether to biopsy. A biopsy gives the answer. Caught early, most skin cancers, including melanoma, can be treated well.

Primary AI can show you the guideline and study sources behind this topic in plain language, so you can bring better questions to your appointment.