Moles and skin tags form through completely different biological processes, even though they often get lumped together as common skin growths. Moles develop from pigment-producing cells that cluster together in the skin, while skin tags grow from excess collagen and blood vessels trapped beneath a pocket of skin. Understanding what drives each one can help you make sense of why they appear where they do, why some people get more than others, and when a growth deserves a closer look.
How Moles Form at the Cellular Level
Moles start with melanocytes, the cells responsible for producing the pigment that gives skin its color. Normally, melanocytes are spread evenly throughout the outer layer of skin. A mole forms when a group of melanocytes migrate toward each other and cluster together instead of staying dispersed. Lab studies show that melanocytes seeded onto a skin-like surface begin migrating and form distinct cell clusters within about 72 hours. Interestingly, once these cells cluster, they actually produce less pigment than scattered melanocytes do. A protein called PAX3 plays a central role in keeping these clustered cells in an immature, undifferentiated state, which is why most moles remain stable and benign rather than continuing to grow aggressively.
Most moles that appear after birth (called acquired moles) are triggered by a specific genetic event inside individual skin cells. A mutation in the BRAF gene, most commonly a variant known as V600E, has been found in about 81% of moles tested in research. These mutations are considered early, one-time events: a single melanocyte picks up the mutation, begins dividing, and its daughter cells form a small cluster visible as a mole. Because additional safety mechanisms in the cell prevent unchecked growth, the vast majority of these moles stay harmless.
Why Some People Develop More Moles
Your total mole count depends heavily on genetics and sun exposure, especially during childhood. People with lighter hair, lighter eyes, and fair skin that freckles easily tend to develop significantly more moles. UV radiation is a major driver: research from the Colorado School of Public Health found that very light-skinned children who tan develop more moles than children who don’t, and that much of the preventable risk for melanoma is established during childhood. The number of sunburns you had as a kid, how frequently you were exposed to intense sun, and whether your skin responded by freckling all contribute to the number of moles you carry as an adult.
Hormones also play a role. Pigment cells in the skin have estrogen receptors, so periods of hormonal change, particularly pregnancy, can cause existing moles to darken or shift in shape. This is a normal response to the extra estrogen circulating in the body and usually isn’t cause for alarm, though any mole that changes dramatically is worth having evaluated.
What Causes Skin Tags
Skin tags are structurally simple growths. They form when collagen fibers and tiny blood vessels get enclosed inside a pouch of skin, creating a small, soft, flesh-colored flap that hangs from the surface. The leading mechanical trigger is friction. Skin rubbing against skin or against clothing gradually irritates the area and promotes the overgrowth of tissue. That’s why skin tags cluster in predictable spots: the neck, underarms, groin, under the breasts, on the eyelids, and around the genitals. These are all areas where skin folds meet or clothing creates persistent rubbing.
But friction alone doesn’t explain why some people are covered in skin tags while others never develop a single one. Several growth-signaling molecules drive the process at a deeper level. A signaling protein called TGF-β1 is one of the main promoters of fibroblast proliferation, meaning it pushes the connective tissue cells in the skin to multiply and produce more collagen. Epidermal growth factor and insulin-like growth factor (IGF-1) also contribute. When levels of these growth signals are elevated, the skin is essentially being told to build more tissue than it needs, and skin tags are the result.
The Insulin Resistance Connection
One of the most significant and underappreciated causes of skin tags is insulin resistance. When your body produces excess insulin to compensate for cells that aren’t responding well to it, that surplus insulin activates IGF-1 receptors in the skin. This triggers fibroblast cells to proliferate, directly leading to skin tag formation. Research published in the Journal of the American Academy of Dermatology found a clear association between multiple skin tags and elevated insulin resistance scores. People with a large number of skin tags, particularly in clusters, are statistically more likely to have metabolic syndrome or early-stage type 2 diabetes, even before a formal diagnosis.
This means that if you’ve noticed a sudden increase in skin tags, it may reflect changes in your metabolic health rather than just friction or aging. Skin tags can serve as an external signal of what’s happening internally with blood sugar regulation.
Hormones, Weight, and Age
Pregnancy is a common trigger for both new skin tags and changes in existing moles. The combination of elevated estrogen, increased growth hormone activity, and weight gain creates ideal conditions. Some women notice skin tags appearing for the first time during pregnancy, along with small bright red benign blood vessels on the skin. Hormones in birth control pills can produce similar effects. Many of these growths stabilize or shrink after hormone levels return to baseline, though some persist.
Weight gain at any stage of life increases your risk of skin tags simply by creating more skin folds and more friction. Aging matters too. Skin tags become increasingly common after age 40, likely because cumulative friction exposure, hormonal shifts, and metabolic changes all compound over time. Moles, by contrast, often stop appearing after age 30 to 40. Any new mole that shows up later in life warrants more attention, since the expected window for developing new moles has largely closed by then.
Moles vs. Skin Tags: Telling Them Apart
Moles and skin tags look and feel distinctly different once you know what to look for. A mole is typically flat or slightly raised, round, evenly colored (usually brown or tan), and firmly attached to the skin. A skin tag is soft, flesh-colored or slightly darker, and hangs from the skin by a thin stalk. Moles can form anywhere on the body, while skin tags strongly favor friction zones like the neck, armpits, and groin.
The key concern with moles is the small chance that one could become cancerous. The National Cancer Institute’s ABCDE criteria offer a straightforward way to evaluate any mole that looks different:
- Asymmetry: one half doesn’t match the other
- Border: edges are ragged, notched, or blurred
- Color: uneven shading with multiple tones of brown, black, tan, or patches of red, white, or blue
- Diameter: larger than about 6 millimeters (roughly the size of a pencil eraser), or growing
- Evolving: any visible change over weeks or months
Skin tags, on the other hand, are virtually always benign. They’re a cosmetic nuisance, not a health threat, though their presence in large numbers can point to insulin resistance.
Why DIY Removal Is Risky
Skin tags are vascular, meaning they have their own blood supply and sometimes contain nerve fibers. Cutting one off with scissors or tying it with string at home can cause uncontrolled bleeding, significant pain, and infection. UCLA Health specifically warns against home removal for these reasons. A dermatologist can remove skin tags quickly using freezing, cauterization, or a sterile snip, with minimal risk. The same applies to moles: removing a mole at home means you lose the opportunity to have the tissue examined under a microscope, which is the only way to confirm whether abnormal cells are present.