What Causes Moles to Suddenly Appear? (2024)

Moles, also known as nevi, are very common. Most people have about 10 to 40 moles that form between childhood and adulthood.

A mole occurs as a concentration of skin cells called melanocytes (cells that produce pigment). They may form in response to ultraviolet (UV) light exposure or changing hormone levels.

Though most moles are harmless, you should not ignore them. New moles or moles that change can be signs of melanoma(skin cancer). Early detection is key to successfully treating this fast-spreading type of skin cancer.

This article explains how new moles form, the types of moles, and what mole traits may be signs of skin cancer.

What Causes a New Mole to Appear?

Moles appear when melanocytes in your epidermis (the top layer of skin) become overgrown and develop in groups. While melanocytes are normally present in your body, internal and external factors can trigger changes that result in moles.

Moles begin appearing in childhood and continue throughout your lifetime.

UV Radiation

UV radiation from the sun or tanning beds is a common cause of moles that appear from childhood into adulthood. When exposed to UV light, melanocytes produce melanin (a protective, skin-darkening pigment) and cluster to form moles.

The impact of UV radiation on melanocytes is why most moles occur on parts of your body that receive the most sun exposure. You may notice the eruption of new moles after spending an extended period in the sun.

Hormonal changes

Moles are more likely to occur during periods when your hormones are very active, such as adolescence and pregnancy. These changes are related to the estrogen receptors in pigment cells. When extra estrogen is circulating, it can trigger these receptors and result in hormone-related skin changes like moles.

Certain characteristics

Having the following characteristics increases your risk of new moles appearing throughout your lifetime:

• Family history of moles
• Frequent exposure to sources of UV light, such as sunlight or tanning beds
• Fair skin, since this type of skin produces less protective pigment
• History of severe blistering sunburns
• An abundance of existing moles

Types of Moles

Not all moles are alike. The most common types of moles include the following:

Acquired Moles (Common Moles)

Moles appearing on your skin after birth are called acquired moles. They are also called common moles and are typically harmless. Most adults have between 10 and 40 acquired moles.

Acquired moles usually appear in childhood and early adulthood through age 40, though they can develop anytime. Common characteristics of acquired moles include the following:

• Smaller than the size of a pencil eraser (about 6 millimeters or 1-quarter inch in diameter)
• Smooth surface
• Round or oval shape
• Distinct and even boundaries
• Slightly dome-shaped or raised height
• May have hairs
• Usually located on areas above your waist that receive the highest levels of sun exposure
• Brown, pink, or tan, though the color can be darker in people with dark skin
• Low risk of causing skin cancer
  

Congenital Moles

Congenital moles develop in the womb and are present at birth or during a baby's first year. They occur in about 1% of the population, typically with the following characteristics:

• Size that ranges from less than 1-quarter inch to coverage over your entire body
• Variation in size, shape, color, surface texture, and hairiness in larger congenital moles
• Permanent "goosebump" appearance
• Typically brown though reddish tan to black color is also possible
• Higher risk of becoming skin cancer than common moles, especially among giant congenital moles (larger than 8 inches in width)
• Grow in proportion to a child's growth
  

Atypical Moles (Dysplastic Nevi)

Atypical moles, also called dysplastic nevi or Clark's nevi, are present in about 10% of people in the United States. These moles typically have the following characteristics:

• Larger than a common mole, typically bigger than the size of a pencil eraser (about 6 millimeters or 1-quarter inch in diameter)
• Tan to dark brown color on a pink background
• Poorly defined or irregular edges that may appear to fade into the skin around the mole
• Typically flat
• Often on the upper torso in areas that get the most sun exposure, but can also appear on the scalp, breasts, and below your waist
• Surface feel that is smooth, slightly scaly, or pebbly
• Typically benign (non-cancerous), though the risk of skin cancer increases with the number of atypical moles present
  

Spitz Nevus

A Spitz nevus is a rare, benign mole that is usually acquired. It often has some of the same features as melanoma. A Spitz nevus so closely resembles a melanoma that it can't be identified visually. A Spitz nevus often has the following characteristics:

• Different colors like black, red, and brown
• Possible bleeding
• An opening that oozes
• Develops in the first 20 years of life and occasionally into adulthood

Mole Changes and Warning Signs

While most moles, brown spots, and other skin growths do not pose a health threat, some represent the first warning signs of melanoma.

Benign moles do not typically change in shape, size, or texture. Certain changes to existing moles, the appearance of a new mole, or the eruption of a spot that looks different from the other spots (known as the "ugly duckling" sign) can be early warning signs of skin cancer.

Melanomas

Use the ABCDE rule to identify possible signs of melanoma. Contact your healthcare provider about any mole that has one or more of the following characteristics:

• A: Asymmetry: Melanomas are typically asymmetrical. The two halves don't match if you draw a line through the middle of the mole.
• B: Border: Melanomas are often uneven. They may have uneven, scalloped, blurred, or notched edges.
• C: Color: A mole with multiple colors, different shades of brown, tan, or black mixed with white, gray, red, or blue, can be a warning sign of melanoma.
• D: Diameter: While melanomas can be very small, they are often larger than a pencil eraser (about 6 millimeters or 1-quarter inch across).
• E: Evolving: A mole that evolves in appearance and/or size may be a cause of concern.

Skin Self-Checks

Performing regular skin self-checks can help you identify mole changes and signs of melanoma early. Doing this can improve your chances of getting early and successful treatment. Most skin cancers are highly curable when diagnosed and treated early.

While there is no consensus regarding how often you should perform a skin self-check, the Skin Cancer Foundation advises performing them at home monthly. Your healthcare provider can advise on how often you need skin self-checks based on your risk factors for skin cancer.

Before doing your first skin self-check, look at photos of melanoma in different stages to know the features of a suspicious mole. Record the patterns of freckles, moles, and blemishes to compare changes in later months.

To perform a skin self-check, use a well-lit room. Stand in front of a full-length mirror without clothing. Use this process to perform a comprehensive exam:

• Examine your face with careful attention to your nose, lips, inside your mouth, and the back and front of your ears.
• Move hair away from your scalp using a hair dryer or comb to examine small sections until you have examined the entire surface of your scalp.
• Use the full-length mirror to examine the front of your neck, chest, and abdomen. Raise your arms to examine the sides of your upper body.
• To examine the back of your body, turn away from the full-length mirror. Use a handheld mirror to observe your back, the back of your neck, shoulders, buttocks, and the backs of your thighs.
• Sit on a chair and use the handheld mirror to examine your genitals. Continue to observe the backs of your legs, the insides of your thighs, the tops and soles of your feet, your toenails, and between your toes.

In addition to performing monthly skin self-checks, the Skin Cancer Foundation advises that you see a dermatologist annually for a total body skin examination. If you have a high risk of skin cancer, you may be advised to have these types of professional exams more frequently.

When to Contact a Healthcare Provider

About 50% of melanomas are self-detected. When melanoma is detected and treated before it spreads to the lymph nodes, there is a 99% survival rate.

A mole that fits the ABCDE criteria should be reported to your healthcare provider. A healthcare provider should also examine moles with any of the following characteristics:

• New moles
• Moles that do not resemble any others on your body
• Moles or other sores that do not heal
• Swelling or redness beyond the border of a mole
• Color that spreads from the border of a spot into the surrounding skin
• Tenderness, itching, or pain in a mole that persists or goes away then returns
• Changes in the texture or surface of a mole that can include oozing, scaliness, bleeding, or the appearance of a lump or bump
  

Summary

Moles are common skin growths that consist of clusters of melanocytes. They often grow in response to hormonal changes or UV light exposure. While most moles are benign and harmless, some moles occur as the first sign of skin cancer.

A healthcare provider should examine moles that change in size, shape, or texture. New bleeding or itching at the site of a mole should also be checked.

Monthly skin self-checks can help you find the changes that may lead to problems. Finding mole changes and getting prompt treatment can increase your chances of curing skin cancer when it exists.