Blue Nevus
A usually harmless blue-colored mole caused by deep skin pigment
Quick Facts
- Type: Benign pigmented skin growth (mole)
- Color: Blue, blue-gray, or blue-black
- Common sites: Hands, feet, scalp, face, buttocks
- Cancer risk: Usually benign; rare types need evaluation
Overview
A blue nevus is a type of mole that looks blue, blue-gray, or blue-black. The unusual color comes from clusters of pigment-producing cells (melanocytes) located deep within the skin. When brown melanin pigment sits deep in the skin, the way light scatters makes it appear blue to the eye, an effect known as the Tyndall effect.
Most blue nevi are small, stable, and completely harmless. They are usually present from childhood or appear in adolescence or early adulthood and remain unchanged for life. A few uncommon variants can be larger or behave differently, so any blue mole that is new, growing, or changing should be evaluated by a doctor to make sure it is not a more serious lesion.
Symptoms
A typical blue nevus has a distinctive but stable appearance:
- A small, well-defined spot or slightly raised bump, often a few millimeters across
- A blue, blue-gray, or blue-black color, sometimes appearing steel-blue
- A smooth surface and a round or oval shape with even borders
- Common locations including the backs of the hands and feet, scalp, face, and buttocks
A common blue nevus does not usually cause symptoms. Features that should prompt evaluation include a lesion that is new in adulthood, growing, changing color or shape, becoming irregular, itching, bleeding, or larger than about a centimeter.
Causes
A blue nevus forms when melanocytes collect deep in the dermis (the layer beneath the skin's surface) instead of near the top of the skin as in an ordinary brown mole. The deep location of the dark pigment is what produces the blue appearance.
The exact reason these cells gather in this way is not fully understood. Blue nevi are generally considered a normal variation rather than the result of an identifiable cause, and most arise on their own without any clear trigger. They are not contagious and are not caused by injury or sun exposure in the way some other skin spots are.
Risk Factors
- Blue nevi are common and can occur in anyone
- They often first appear in childhood, adolescence, or early adulthood
- There are no strong lifestyle risk factors for the common, harmless type
- A new blue nevus appearing later in adult life warrants closer attention
Diagnosis
A doctor or dermatologist can usually recognize a typical blue nevus by its appearance, but assessment may include:
- Skin examination and dermoscopy: Inspecting the lesion closely, often with a handheld magnifier, to evaluate its color and structure.
- Skin biopsy: If the lesion is atypical, new, growing, or changing, a sample may be removed and examined under a microscope to confirm it is benign and rule out melanoma.
Treatment
Most blue nevi need no treatment:
- Observation: A typical, stable blue nevus can simply be left alone and watched for changes.
- Removal: A blue nevus may be removed surgically if it is changing, atypical, in a spot where it is repeatedly irritated, or if the diagnosis is uncertain and melanoma needs to be excluded.
When removed, the lesion is examined under a microscope to confirm the diagnosis. Treatment for the rare malignant variants follows melanoma care.
Prevention
- Blue nevi cannot generally be prevented, as they are usually a normal skin variation
- Practice good general sun protection for overall skin health
- Become familiar with your skin and your existing moles
- Note and report any new, growing, or changing pigmented spots
- Have regular skin checks if you are at higher risk for skin cancer
When to See a Doctor
See a doctor or dermatologist if a blue-colored mole:
- Is new, especially if it appears in adulthood
- Is growing or changing in size, shape, or color
- Has an irregular border or uneven color
- Itches, bleeds, or becomes painful
- Is larger than about a centimeter
Having a new or changing pigmented lesion checked promptly helps ensure that any serious lesion is caught early.
Frequently Asked Questions
Why is a blue nevus blue?
A blue nevus looks blue because the pigment-producing cells sit deep in the skin. When dark brown pigment lies deep down, light scatters in a way that makes it appear blue to the eye, an effect known as the Tyndall effect.
Is a blue nevus dangerous?
Most blue nevi are completely harmless and stay unchanged for life. A few uncommon variants can be larger or behave differently, so any blue mole that is new in adulthood, growing, or changing should be checked by a doctor to rule out melanoma.
Should a blue nevus be removed?
Usually not. A typical, stable blue nevus can simply be watched. Removal is considered if the lesion is changing, atypical, frequently irritated, or if the diagnosis is uncertain and melanoma needs to be excluded.
When should I worry about a blue mole?
See a dermatologist if a blue mole is new in adulthood, growing, changing color or shape, developing an irregular border, itching, bleeding, or larger than about a centimeter. These features warrant evaluation.
Can a blue nevus turn into cancer?
Common blue nevi are benign and very rarely cause problems. There are rare malignant variants, which is why a doctor evaluates any blue lesion that looks unusual or changes over time. Early evaluation ensures any serious lesion is caught.
References
- American Academy of Dermatology Association. Moles.
- MedlinePlus, U.S. National Library of Medicine. Moles.
- Mayo Clinic. Moles — Symptoms and causes.
- Skin Cancer Foundation. Melanoma warning signs.