A halo nevus, also known as Sutton’s nevus, is a common, non-cancerous skin condition characterized by a mole surrounded by a distinct, symmetrical white ring. This phenomenon represents a localized immune reaction within the skin. While usually benign and requiring no treatment, understanding its appearance and underlying cause can help distinguish it from more concerning skin changes.
Defining the Appearance of a Halo Nevus
A halo nevus presents visually as a central, pigmented mole encompassed by a pale, unpigmented circle of skin. The central mole, or nevus, is typically round or oval and has a uniform color, usually brown or pink. The surrounding white ring, or halo, is often about 0.5 to 1.0 centimeter wide and is characteristically symmetrical around the mole. This condition is seen most frequently in healthy children and teenagers, though it can occur in young adults. It is estimated to affect approximately one percent of the general population. Halo nevi are most commonly found on the trunk, which includes the chest, abdomen, and back. A person may develop just one halo nevus, but it is also common to have multiple lesions appear over time.
Understanding the Immune System’s Role
The formation of the halo is the result of a targeted, localized autoimmune response against the mole’s pigment-producing cells, called melanocytes. Specialized immune cells, specifically a type of white blood cell known as CD8+ T lymphocytes, migrate to the area around the mole. These cells mistakenly identify the melanocytes in the nevus as foreign invaders and begin to destroy them. This destruction of melanocytes leads to the loss of pigment not only within the mole itself but also in the surrounding ring of skin. The resulting depigmentation creates the bright white halo that gives the nevus its name. This immune-mediated destruction can be triggered by factors such as intense sun exposure or local trauma to the mole.
Clinical Assessment and Confirmation
The primary reason to seek medical attention for a halo nevus is to ensure it is not a form of skin cancer, such as a regressing melanoma. While halo nevi are benign, a melanoma that is undergoing regression can also be surrounded by a white or hypopigmented area, making professional assessment necessary. A dermatologist will perform a differential diagnosis to confirm the lesion’s benign nature. A true halo nevus features a central mole with even borders and a halo that is uniformly distributed and perfectly circular. In contrast, the depigmentation surrounding a regressing melanoma is usually irregular in shape and variable in width. Doctors often use a handheld magnification tool called a dermatoscopy to examine the mole’s structure and color patterns. If the lesion appears suddenly in an older adult or shows atypical features like asymmetry or color irregularity, a biopsy may be performed to definitively rule out malignancy.
What to Expect for Long-Term Management
Once a halo nevus is confirmed to be benign, the management strategy involves monitoring rather than active treatment. The natural course of a halo nevus is one of spontaneous regression, meaning the mole and halo will disappear on their own. This process involves four stages, beginning with the formation of the halo, followed by the central mole fading to pink and then disappearing completely. The final stages involve the white patch persisting for a time before gradually repigmenting and returning to the skin’s normal color. This involution process is often prolonged, taking an average of several months to years to complete. Patients are advised to observe the lesion and return for a reevaluation if any concerning changes occur, such as itching, pain, or significant irregularity.