Nevi are common skin growths, often called moles or birthmarks, formed by clusters of pigment-producing cells called melanocytes. These lesions can appear anywhere on the body and vary in size, shape, and color. While most nevi are benign, they present a wide range of appearances depending on their type and location. Benign nevi are typically uniform in color, round or oval-shaped, and symmetrical.
Understanding Different Types of Nevi
Nevi are broadly categorized into congenital nevi, present at birth or appearing within the first year of life, and acquired nevi, which develop later. Congenital nevi can vary significantly in size, color, and texture, sometimes covering large areas of the body. Acquired nevi are common, with most individuals having between 10 and 40, typically developing during childhood and adolescence.
Several common types of acquired nevi exist, distinguished by melanocyte location within the skin. Junctional nevi are flat and darkly pigmented, with melanocytes confined to the junction between the epidermis (outer skin layer) and the dermis (inner skin layer). These are often brown with well-defined borders and common on sun-exposed areas. Compound nevi feature melanocytes both at the dermo-epidermal junction and deeper within the dermis, often appearing slightly raised and pigmented. Dermal nevi, also called intradermal nevi, have melanocytes located entirely within the dermis; they are elevated, flesh-colored or lightly pigmented, and can be dome-shaped. They may become more apparent during puberty and can sometimes have hair growing from them. Blue nevi are characterized by their distinct blue to blue-black color, resulting from the deep location of melanocytes in the dermis, causing light to scatter and produce a blue hue. They are usually firm and can be flat or dome-shaped, commonly found on the hands, feet, scalp, or buttocks.
Factors Contributing to Nevi Formation
Nevi development is influenced by the proliferation of melanocytes, cells responsible for producing melanin, the pigment that gives skin its color. These cells cluster to form the moles. Nevi formation is influenced by both an individual’s genetic makeup and environmental factors.
Genetic predisposition plays a role, as individuals with a family history of many moles often have more themselves. Up to 68% of the variation in nevus density can be attributed to genetic factors. Environmental factors, particularly sun exposure, also contribute to nevus formation. Both chronic and intermittent sun exposure, especially during childhood, can increase the number of nevi. Hormonal changes, such as those during puberty or pregnancy, can also influence the appearance or number of existing moles, causing them to enlarge or darken.
Identifying Concerning Nevi
Recognizing changes in nevi is important for early detection of potential concerns like melanoma, a serious form of skin cancer. While most moles are benign, any new, changing, or unusual mole warrants attention. The “ABCDEs of melanoma detection” is a widely used guide for self-examination.
- A for Asymmetry: The two halves of the mole do not match.
- B for Border irregularity: Benign moles have smooth, even borders, while concerning moles may have uneven, ragged, or notched edges.
- C for Color variation: A mole with multiple shades of brown, tan, black, or areas of white, gray, red, or blue can be a warning sign.
- D for Diameter: A mole larger than 6 millimeters (about the size of a pencil eraser) is a warning sign, though melanomas can be smaller.
- E for Evolving: Any change in size, shape, color, elevation, or new symptoms like bleeding, itching, or crusting.
Regular self-examination using these criteria helps individuals monitor their skin.
Medical Evaluation and Management
When a nevus exhibits concerning characteristics, a medical evaluation by a dermatologist is recommended. This begins with a thorough visual inspection of the skin. Dermatologists may use a dermoscope, a handheld device providing a magnified, illuminated view of the mole’s structures beneath the skin surface, to differentiate between benign and suspicious lesions.
If a nevus appears suspicious, a biopsy is often performed to obtain a tissue sample for microscopic examination. This involves removing the entire mole or a portion, which a pathologist then analyzes for cancerous cells. For benign nevi, no treatment is necessary unless they cause cosmetic concern or irritation. Suspicious or confirmed malignant nevi are managed with surgical removal, often done in an office setting. Early detection and removal are important for better outcomes if melanoma is present.