Skin moles come in a variety of shapes and sizes.
They also come with a variety of questions, including: When should you worry about moles on your skin?
"Most skin moles are normal, but, unfortunately, the worst-case scenario with a mole is melanoma — an aggressive, highly deadly form of cancer," says Dr. Ming Jih, a dermatologist at Houston Methodist.
There's some good news here, though. Although there are rare cases of rapidly growing melanomas, most melanomas grow very slowly — over the course of several years — during which time the mole changes in ways that often can be spotted by eye.
This highlights the importance of knowing the features that make a mole concerning and what to do if you spot one.
What is a skin mole?
"The simplest way to explain a mole is as a collection of melanocytes, which are cells that are responsible for producing skin color, eye color and hair color," explains Dr. Jih. "Melanocytes are normally present throughout the body — when a group of these cells clusters, you get a visible growth known as a mole."
Sometimes a skin mole is present at birth, called a birthmark. But not all birthmarks are moles.
"A birthmark is anything on the skin that's present at birth or occurs soon after birth," says Dr. Jih. "They can be moles, but they can also be skin discolorations caused by a cluster of improperly formed blood vessels, known as vascular birthmarks; some other type of pigmented spot on the skin that's not a mole; or even just abnormal growth of other skin tissues."
And most moles aren't birthmarks. You develop them over the course of your life.
"The largest number of moles usually form during childhood and up through early adulthood, but you can develop new moles throughout your entire life — especially if you have excessive ultraviolet exposure," adds Dr. Jih.
You can also develop skin spots that resemble moles as you age, by the way — such as skin tags and red moles, called cherry angiomas, that are caused by clusters of blood vessels.
What causes moles on the skin to form?
One of the primary causes of the skin moles that form after birth is exposure to ultraviolet (UV) radiation from either the sun or man-made sources, like tanning beds.
When the skin is exposed to UV rays, melanocytes produce a protective, skin-darkening, pigment called melanin. UV exposure can also induce these melanocytes to cluster, creating moles.
This means that the more your skin is exposed to sunlight or other sources of UV light, the more moles you're likely to have as a result.
Certain people are also more likely to develop moles.
"A person can be genetically predisposed to developing more moles, and usually he or she will have family members that easily develop moles, too," says Dr. Jih. "People who have fairer skin are also more likely to develop moles — especially with increased UV exposure — since they produce less protective pigment."
It's important to know how skin moles form since it helps us understand why some are concerning.
Which are the skin moles to worry about?
The reason we're even worried about skin moles in the first place is that, sometimes, a mole can progress into skin cancer — the deadliest form, at that: melanoma.
This happens because the same UV rays that help induce a mole to form can also damage the DNA inside of melanocytes, leading to changes that result in cancer.
Most moles, however, are normal and won't ever develop into melanoma. So how can you tell a normal mole from a concerning one?
"A normal mole should be stable, with a regular, even color (brown, tan or black) and shape (round or oval) that doesn't change," says Dr. Jih. "To determine whether a mole is concerning, I recommend following the ABCDEs, which classify a mole based on asymmetry, border, color, diameter and whether it's evolved over time."
Specifically, the ABCDEs stand for:
- A: Is the mole asymmetrical?
- B: Does the mole have irregular borders?
- C: Is the mole unusually dark, have an atypical color or many colors?
- D: Is the diameter larger than 6 millimeters?
- E: Has the mole's appearance evolved (changed)?
Once every few months, says Dr. Jih, stand in front of a full-length mirror and inspect the moles on your skin while asking yourself these ABCDEs.
"Look at every surface you can see on the front of your body, including your arms, legs and belly, and don't forget to check your palms and the bottoms of your feet," says Dr. Jih. "You'll also want to examine your nails and feel around on your scalp. Checking your backside is trickier. You'll either need to add a handheld mirror or to have a family member help you. Here again, check everywhere."
Dr. Jih says the most objective way to perform this self-check is to document your moles each time, taking photos so that you can compare how a mole currently looks to what it looked like in the past.
When should you see a dermatologist for a mole?
If you answered "Yes" to any of the ABCDEs, make an appointment with a dermatologist to have the mole evaluated.
At a dermatology visit, the following topics will be discussed:
- Your personal medical history
- Your UV exposure history, including how many sunburns you've had
- Whether you have a family history of skin cancer
"If there's a single mole you're worried about, the visit may just be the dermatologist examining the mole by eye but typically also with a special magnifying lens," says Dr. Jih. "This process will help determine whether the mole likely needs to be biopsied or not."
A biopsy is where the mole is removed and sent to be checked under a microscope by a pathologist. If the biopsy results look abnormal, your dermatologist will discuss additional treatment options with you.
"Getting a concerning mole evaluated is important since early detection of melanoma is critical for saving lives and avoiding unnecessary and more aggressive treatments and procedures," says Dr. Jih. "Ideally, we find it while it's still precancerous and it becomes just a simple skin mole removal."
If you're prone to developing moles, you can also schedule regular full-body skin exams at which your dermatologist will scan you from head to toe.
"While rare, melanoma can sometimes develop in just a few months, rather than several years," says Dr. Jih. "What's more is that, in these cases, it's generally a smaller mole that is rapidly changing, but these changes are harder to spot. This is where skin checks by a dermatologist become an important part of early detection."
Can you prevent a mole from progressing into melanoma?
"I think a lot of people underestimate just how much ultraviolet light, both normal sunlight and also from tanning beds, contributes to not only increasing numbers of moles but also the formation of melanoma," says Dr. Jih. "It's so important to protect your skin."
You can protect your skin from UV rays by:
- Limiting unprotected sun exposure
- Applying a broad-spectrum sunscreen with an SPF of at least 30 to your face and other sun-exposed areas, including the neck, chest and backs of hands, when you leave your home
- Applying a broad-spectrum, water-resistant sunscreen with an SPF of at least 35 when you go to the beach or otherwise spent significant time in the sun, reapplying every two hours and after swimming or sweating
- Wearing sun-protective items, such as wide-brimmed hats, UV-blocking sunglasses and long sleeves
- Taking shade breaks when you're out in the sun for extended periods of time
- Avoiding using tanning beds and exposing your skin to other man-made sources of UV light