A mole (melanocytic nevus) is a common skin growth formed when pigment-producing cells, called melanocytes, cluster together instead of distributing evenly. While most moles are harmless, their appearance can sometimes signal a serious health concern, such as melanoma, an aggressive form of skin cancer. Understanding the characteristics of a normal mole compared to a potentially dangerous one is important for early detection and better health outcomes.
The Biology of Moles and Common Types
Moles represent a benign proliferation of melanocytes, often initiated by genetic mutations that cause the cells to multiply. After this initial growth phase, the cells typically enter a state of growth arrest, which is why most moles remain stable throughout a person’s life.
A common acquired mole appears after birth, typically in childhood or early adulthood, and is generally small, symmetrical, and uniformly colored. Junctional nevi are flat and brown, with melanocytes clustered at the border between the outer and deeper layers of the skin. Compound nevi are slightly raised and have melanocytes in both the superficial and deeper skin layers.
Moles present from birth are called congenital nevi. Others are classified as atypical or dysplastic nevi, which are larger than common moles, often have irregular borders, and display color variation. Although an atypical mole itself is usually benign, having them is a risk factor for developing melanoma elsewhere on the body.
The ABCDE Guide to Self-Screening
Regular self-examination using the ABCDE guide provides a framework for monitoring skin growths for signs of malignancy. This mnemonic focuses on five key changes in a mole’s appearance that warrant professional evaluation. Observing one or more of these features means consulting a medical professional.
Asymmetry
A benign mole is typically symmetrical; if you were to draw a line through the center, the two halves would essentially match. Asymmetry, or a lack of matching halves, is a potential sign of melanoma. When a mole’s growth becomes uncontrolled, as in cancer, the resulting shape is often irregular and unbalanced.
Border Irregularity
Common moles have smooth, distinct, and well-defined borders that clearly separate the mole from the surrounding skin. A suspicious growth often presents with a border that is irregular, scalloped, notched, or poorly defined. This uneven edge results from the cancerous cells spreading laterally through the skin layers.
Color Variation
Normal moles usually exhibit a single, uniform shade of tan, brown, or black throughout the lesion. Color variation within a single mole is a significant warning sign. This variation can include multiple shades of brown, black, red, white, or blue, reflecting the different growth patterns and depths of the cancerous cells.
Diameter
The majority of melanomas are greater than 6 millimeters in diameter when diagnosed, which is roughly the size of a pencil eraser. While size alone is not definitive, any mole exceeding this measurement should be viewed with suspicion. Melanomas can sometimes be smaller than 6 millimeters, especially in the earliest stages.
Evolving
The most important sign is evolution, which refers to any change in a mole over time, including changes in size, shape, color, or elevation. A mole that begins to itch, bleed, crust, or feel tender is also considered evolving and requires immediate medical attention. Any mole that looks significantly different from all the others on your body (the “ugly duckling” sign) should be evaluated.
Advanced Risk Factors and Prevention
Risk factors for melanoma include a person’s genetic background and sun exposure history. Individuals with a first-degree relative (a parent, sibling, or child) who has had melanoma face an increased risk, as approximately one in ten people with the disease have a family history. Having a high number of common moles, generally considered 50 or more, also elevates the lifetime risk of developing melanoma.
A fair complexion, including light skin, blue or green eyes, and red or blond hair, increases susceptibility because the skin produces less protective melanin pigment. A history of severe, blistering sunburns, particularly during childhood or adolescence, is strongly linked to a higher risk of skin cancer later in life. Using indoor tanning beds, which emit intense ultraviolet radiation, also increases risk.
Prevention centers on reducing exposure to ultraviolet (UV) radiation from the sun and artificial sources.
- Wear broad-spectrum sunscreen with an SPF of 30 or higher.
- Apply sunscreen 30 minutes before going outside and reapply every two hours.
- Seek shade, especially between 10 a.m. and 4 p.m. when UV rays are strongest.
- Wear protective clothing, such as wide-brimmed hats and sunglasses.
Professional Examination and Removal
If a mole displays any concerning ABCDE features, the next step involves a professional examination by a dermatologist. During this check, the physician will examine the mole using a handheld device called a dermatoscope, which provides a magnified, illuminated view of the mole’s underlying structure. This allows for a more accurate assessment of the pigment network and cell arrangement.
If the mole remains suspicious, a biopsy is performed to obtain a tissue sample for laboratory analysis. The two main methods are shave removal, which shaves the lesion flush with the skin surface for superficial growths, and excisional biopsy.
An excisional biopsy involves surgically removing the entire mole along with a small margin of surrounding healthy tissue, requiring stitches to close the wound. This method is preferred for deeply suspicious lesions to ensure the pathologist can fully examine the depth of the cells. If the biopsy confirms melanoma, a wider surgical excision is often performed to remove any remaining cancer cells.