Blue nevi are a type of mole or birthmark characterized by their blue-gray to blue-black color. These lesions arise from melanocytes, pigment-producing cells located deeper within the skin’s dermis, unlike common brown moles found in the more superficial epidermis. The unique blue hue results from the Tyndall effect, where shorter blue wavelengths of light are scattered by the deeply situated melanin. Though benign, knowing their characteristics and potential changes is important for skin health.
Understanding Their Appearance and Types
Blue nevi often appear as a single, well-defined bump with a smooth surface, or as flat macules or plaques. Their color ranges from steel-blue to bluish-black, sometimes appearing brown or yellowish. These moles are commonly found on the extremities, such as the back of the hands and feet, but can also appear on the scalp, face, buttocks, and sacral region. Their size ranges from 0.5 to 1 centimeter in diameter for common types.
There are two primary types of blue nevi: common blue nevi and cellular blue nevi. Common blue nevi are small, solitary, and remain unchanged throughout a person’s life. In contrast, cellular blue nevi are larger, often exceeding 1 centimeter in diameter, and are more nodular or raised. Cellular blue nevi can have a higher cellular density and may involve the superficial subcutis.
Assessing Risk and Signs to Watch For
Blue nevi are benign, and common blue nevi have a low risk of malignant transformation. However, cellular blue nevi, though largely benign, carry a rare chance of developing into a malignant blue nevus, a type of melanoma. This rare transformation can lead to an aggressive form of skin cancer. Melanoma can also arise de novo with features resembling a blue nevus.
Given this risk, self-monitoring for changes in a blue nevus is important. Signs that warrant medical attention include changes in size, shape, or color. Irregular borders, bleeding, itching, or pain are also concerning indicators. A blue nevus that grows larger than 6 millimeters or 1 centimeter, develops an irregular border, changes in color, or becomes elevated should be evaluated by a healthcare professional. The appearance of a new blue nevus in adulthood, especially after age 30, also warrants a medical assessment.
Diagnosis and Management
Blue nevi are diagnosed through visual inspection by a healthcare provider, often supplemented with dermoscopy. Dermoscopy is a non-invasive tool that uses magnification and polarized light to examine skin lesions, revealing characteristic patterns, such as homogeneous bluish or steel-blue pigmentation, helping differentiate blue nevi from other lesions, including melanoma. Despite its utility, dermoscopy is not a substitute for a biopsy if there is diagnostic uncertainty.
If a blue nevus shows suspicious changes, a biopsy is performed for definitive diagnosis. This involves removing a small sample of the lesion for microscopic examination to check for cancer cells. For stable, benign blue nevi, management involves observation without intervention. However, surgical removal may be recommended for cosmetic reasons, if there is diagnostic uncertainty, or if changes suggest potential malignancy. While rare, blue nevi can recur at the site of removal, requiring further evaluation.