Understanding the White Ring
A mole encircled by a distinct white or depigmented ring is medically termed a halo nevus, also known as Sutton’s nevus. This appearance features a central pigmented mole, which can be brown, black, or blue, surrounded by a symmetrical white halo of skin. The white ring typically measures about 0.5–1.0 cm in width and is round or oval. Over time, the central mole may progressively fade, eventually disappearing entirely and leaving only the white patch. This phenomenon is observed in approximately 1% of the white-skinned population, commonly affecting healthy children and young adults, though it can also occur at older ages.
The Immune System’s Role
The formation of the white ring around a halo nevus is attributed to an immune response within the body. The immune system identifies the pigment-producing cells, called melanocytes, within the mole as foreign. Specialized white blood cells target and destroy these melanocytes in the skin surrounding the mole. This attack leads to a localized loss of pigment, resulting in the white halo.
Is It Something to Worry About?
Halo nevi are almost always benign, meaning they are non-cancerous and generally harmless. While common, particularly in children, a white ring around a mole could, in rare instances, signify the body’s reaction to a more concerning lesion, such as melanoma. This is uncommon, but professional evaluation is important, especially if the halo nevus appears in adulthood. Melanoma, a type of skin cancer, can sometimes exhibit similar depigmentation as the immune system attempts to attack it. However, such cases often present with atypical features in the mole itself, such as irregular structure or color, distinguishing them from benign halo nevi.
When to See a Doctor
While most halo nevi are harmless, seeking medical evaluation from a dermatologist or general practitioner is advisable for any new or changing mole. This is especially important if the white ring is not uniform, or if the mole itself displays unusual characteristics. Warning signs that warrant professional assessment include asymmetry, irregular borders, varied color, a diameter larger than 6 millimeters, or any evolution in size, shape, or symptoms like itching or bleeding. A doctor can properly diagnose the mole and rule out any more serious conditions, providing reassurance and appropriate guidance.