An acral nevus is not cancer. It is a benign mole that appears on the palms, soles, or under the nails. These moles are common and harmless in the vast majority of cases. However, acral lentiginous melanoma, a rare skin cancer, develops in the same locations, which is why any new or changing spot on your palms or soles deserves attention.
What an Acral Nevus Actually Is
An acral nevus is simply a mole that forms on acral skin, the thick, hairless skin of your palms, soles, fingers, and toes. These moles contain clusters of melanocytes, the cells that produce pigment. They can appear at any age, though certain patterns are more common at different life stages. In younger people, acral nevi tend to show a “double line” pigment pattern, while in older adults, single-line patterns are more typical. The average age of people with acral nevi in one large study was about 30, but they occur across all age groups from early childhood onward.
Acral nevi are especially common in people with darker skin tones. They typically appear as small, evenly colored brown or tan spots, usually less than 6 millimeters across, with a regular shape and stable appearance over time.
How It Differs From Acral Melanoma
Acral lentiginous melanoma (ALM) is the cancer that can mimic an acral nevus. It is rare overall, with incidence rates between 1.5 and 2.8 per million people depending on racial and ethnic background. But it accounts for a disproportionate share of melanomas in people of color. Among non-Hispanic White individuals, ALM represents only about 0.8% of all melanomas. Among Hispanic Black, American Indian/Alaska Native, and Asian/Pacific Islander populations, that figure jumps to 19.1%.
The critical visual differences come down to regularity. A benign acral nevus has evenly distributed pigment, symmetrical borders, and a consistent color. Under dermoscopy (a magnified skin exam), benign moles on the soles and palms show pigment lining up neatly along the skin furrows, the tiny grooves in your skin’s surface. This is called a parallel furrow pattern, and it is the hallmark of a normal acral mole.
Acral melanoma does the opposite. Its pigment tends to concentrate along the ridges of the skin rather than the furrows. Colors are uneven and patchy, with mixtures of brown, black, gray, or even pink. The borders look irregular, and the pigment distribution across the lesion is chaotic rather than orderly. In one comparative study, every benign acral nevus examined showed regular, evenly spaced pigment patterns, while every melanoma showed irregular distribution of colors and structures.
Warning Signs to Watch For
The standard ABCDE checklist applies to acral lesions, with some specific considerations for palms, soles, and nails:
- Asymmetry: the two halves of the spot don’t match
- Border: edges are jagged, blurred, or uneven
- Color: multiple shades or colors within the same spot, especially combinations of black, brown, white, gray, or pink
- Diameter: larger than 6 millimeters (about the size of a pencil eraser)
- Evolving: any change in size, shape, or color over weeks to months
For nail lesions specifically, acral melanoma often appears as a dark brown or black streak running lengthwise through the nail, most commonly on the thumb or big toe. As it progresses, the nail may crack, distort, or partially detach. A new pigmented streak in a single nail that widens over time is one of the more recognizable warning signs.
On the soles, a spot that looks like a bruise or stain but doesn’t fade over several weeks, or a previously flat mole that becomes raised or starts to thicken, warrants a closer look.
What Causes Acral Melanoma
Unlike most skin cancers, acral melanoma is not driven by sun exposure. These lesions develop on sun-shielded areas, and current evidence supports a pathway to cancer that is independent of UV radiation. This is part of why standard sun-safety messaging doesn’t capture the full picture of melanoma risk.
Mechanical stress and trauma have been proposed as potential triggers. Tumors most commonly arise on the foot, and some research suggests that tumor location overlaps with the highest-pressure areas on the sole. A retrospective study of 685 Chinese patients with acral melanoma found an association between prior trauma at the tumor site and disease development. However, the trauma theory remains debated. A separate analysis of 122 acral melanomas from the Mayo Clinic found no significant difference in tumor distribution between weight-bearing and non-weight-bearing regions of the foot.
The current understanding is that acral melanoma is likely multifactorial, involving an interaction between genetic susceptibility and environmental factors such as repeated mechanical injury. No single cause has been confirmed.
Why Early Detection Matters
Acral melanoma carries worse survival rates than other melanoma subtypes, largely because it tends to be diagnosed later. People don’t routinely check the soles of their feet, and dark streaks in nails are easily dismissed. The overall five-year survival rate for acral melanoma is about 78%, but outcomes vary dramatically by stage. Stage I disease has a 93.8% five-year survival rate. By stage II, that drops to 76.2%. Stage III sits at 63.4%.
What makes these numbers particularly important is that stage II acral melanoma doesn’t behave like stage II melanoma elsewhere on the body. In general cutaneous melanoma, stage II is still associated with relatively good outcomes. For acral melanoma, the drop-off is steeper. Tumor thickness and whether cancer has reached the lymph nodes are the two strongest predictors of survival. Thicker tumors at diagnosis and positive lymph nodes each independently worsen the prognosis.
The five-year recurrence-free survival rate also tells a revealing story. For stage I, it’s about 90%. For stage II, it falls to 50%. This means that even among people whose acral melanoma is surgically removed, half of those with stage II disease experience a recurrence within five years.
When a Biopsy Is Needed
If you notice a pigmented spot on your palm, sole, or under a nail that looks suspicious or has changed recently, a dermatologist can evaluate it with dermoscopy. This painless exam uses a magnifying device to examine the pigment patterns in the skin. A trained eye can often distinguish the orderly furrow patterns of a benign nevus from the chaotic ridge patterns of melanoma.
If the dermoscopic appearance is ambiguous, or if a pigmented lesion doesn’t respond to a short course of treatment for a suspected benign condition (like a fungal infection or wart), a biopsy is the next step. The goal is tissue confirmation, because visual assessment alone, even with dermoscopy, has limits. This is especially true in the early stages of acral melanoma, where the fibrillar patterns can closely resemble those of a benign mole.
Routine self-checks of your palms, soles, nail beds, and the spaces between your toes take less than a minute and are the simplest way to catch changes early. Pay particular attention to any spot that is new, growing, multicolored, or unlike your other moles.