[Health Byte] That Mole You Have Might Be Cancer...

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Different Types of Moles

Almost everyone has moles. But not all moles are created equal. Some are completely harmless, while others carry a risk of developing into melanoma (the most aggressive and dangerous form of skin cancer). Knowing the difference matters. Also, fun fact, moles that you have now that aren't cancerous, can turn into something to worry about.

Broadly speaking, doctors divide moles into two categories: common moles and dysplastic moles.

First things first, what is a mole?

A mole is a common skin growth caused by a cluster of melanocytes (the cells that produce melanin, the pigment that gives skin its color).

Instead of being evenly spread out, these pigment-producing cells group together in one spot, forming a visible mark on the skin. That's what you see as a mole. Usually they appear in childhood and adolescence, but some can appear later in life, especially due to sun exposure.

Common moles

Common moles are further classified based on where the mole cells sit within the skin.

A junctional nevus (also called a marginal nevus) forms at the junction between the epidermis (the outer layer of skin) and the dermis (the deeper layer beneath it). These moles are usually flat, dark in color, and hairless.

"This type of mole is the most likely to develop cancerous changes," says Dr Li Xin, director of dermatology at Shanghai Yueyang Hospital. "Because they're flat, they're more easily rubbed or irritated."

An intradermal nevus forms when mole cells are located entirely within the dermis (the deeper layer of skin, away from the surface). These moles are benign (non-cancerous), often raised above the skin, and may have hair growing from them.

A compound nevus sits somewhere in between: mole cells are found both at the epidermis-dermis junction and deeper in the dermis. These moles may be slightly raised, but not as prominent as intradermal nevi, and they are generally unlikely to become cancerous.

What doctors worry about most are flat moles – especially those in high-friction areas such as the palms of the hands or the soles of the feet. "Frequent rubbing is a known risk factor for cancerous changes in moles," Li says.

Dysplastic moles

Dysplastic moles (also called atypical moles) look different from common moles. Their shape may still be symmetrical, but their color is often uneven or unusual. These moles deserve extra attention, as they have a higher chance of developing into melanoma.

Why self-checks matter

The takeaway? Regular, careful self-checks are essential. Watching for changes in size, shape, color, or texture can help catch risky moles early – when intervention is simplest and most effective. When in doubt, get it checked.

The ABCD Rule

"There is a simple and easy way, which is called ABCDE rule. We can do self check at home and follow the change of our moles based on the rule," Li said.

A is for Asymmetry

We can compare one half of the mole with the other. If part of the mole is unlike the other half, then this is cause for concern.

B is for Border

Check the border of a mole. If the mole has an irregular, scalloped, or poorly defined border, it is something to get checked.

C is for Color

Check the color of the mole. If the mole has varying colors from one area to the next, such as shades of tan, brown or black, or areas of white, red, or blue, it needs to get checked.

D is for Diameter

We can check the size of the mole and set 6 milliliter as an indication of concern. If the mole's diameter is bigger than 6 millimeters, it needs to get checked.

E is for Evolving

If the mole looks different from the rest or is changing in size, shape, or color or becomes painful or has fluid within a short period of time, get it checked.

If the mole is benign, we just need to continue the regular self check. If some risky changes or conditions are detected, it is important to visit the hospital as soon as possible.

The Risk Factor

If a mole shows any questionable signs, a hospital visit isn't optional – it's essential.

"We recommend coming in for a dermoscopy examination," says Dr Li. (Dermoscopy is a non-invasive test using a special magnifying device that allows doctors to see structures beneath the skin's surface.) "With a dermoscope, we can make a quick and fairly precise judgment about whether a mole has developed cancerous changes."

According to Li, the risk factors for melanoma also differ between Chinese and Western populations, largely due to differences in genetics, lifestyle, and environment. "For Westerners, excessive sun exposure is the biggest risk factor," he explains. "For Chinese patients, frequent friction or rubbing is more significant."

That's why extra care should be taken with moles located in high-contact areas. "For junctional (marginal) nevi on the palms or soles of the feet, I strongly recommend surgical removal to prevent malignant transformation," Li says.

Sun exposure still matters, though – especially ultraviolet (UV) radiation (the invisible rays from sunlight that damage skin cells). Sunbathing and sunburn both increase risk and shouldn't be taken lightly.

For small moles – those under 3 millimeters in diameter – laser therapy may be an option. But Li stresses that this should only be done in a hospital setting. "Laser stimulation itself can sometimes trigger cancerous changes if it's done improperly," he says.

Bottom line: don't self-diagnose, don't DIY treatments, and don't ignore changes. When it comes to moles, professional evaluation is the safest move.

If You Go

Dermatology department of Shanghai Yueyang Hospital at No. 110 Ganhe Rd (甘河路110号)

Outpatient service is available in the mornings and afternoons from Monday to Saturday and Sunday morning.

Health Byte Tips

Shanghai has rolled out a digital vaccination certificate, giving residents access to official vaccination records through the city government's Suishenban (随申办) app.

The system draws from Shanghai's local digital vaccination database and covers not only mainland residents but also expatriates and individuals from Hong Kong, Taiwan, and Macau.

To make things easier for international families and overseas travel needs, the digital certificate is available in multiple languages. In addition to Chinese, records can be viewed in English, French, German and Arabic.

The certificate isn't just a static record. It supports a range of practical functions, including vaccination appointment booking, vaccination history checks, downloading and printing official vaccination documents, and locating vaccination hospitals, according to the Shanghai Health Commission. The goal is to streamline services and reduce paperwork for residents.

For questions or assistance related to the digital vaccination certificate, residents can call the service hotline at 400-836-6086, available daily from 9am to 6pm.

Upcoming Topics

Lung nodule is common problem detected in health checkup. Many people are scared to death after learning that they have lung nodules. What kinds of nodules are risk factor for lung cancer and what kinds are not, let's listen to the experts in the next column. Stay tuned.

About the Author

Cai Wenjun is a seasoned health reporter with Shanghai Daily. With extensive experience covering the local medical system, hospitals, health officials and leading medical experts, Cai has reported on major pandemics including SARS, swine flu and COVID-19, as well as developments in the local health industry.