Acral Nevus: Understanding Moles on Palms, Soles, and Nails

An acral nevus is a melanocytic nevus (mole) located on the acral sites of the body — the palms of the hands, soles of the feet, and the nail apparatus (subungual and periungual areas). These locations are collectively referred to as acral because they represent the extremities or terminal portions of the limbs. Acral nevi deserve special attention in dermatology not because they are inherently more dangerous than moles elsewhere, but because moles in these locations look fundamentally different from moles on other body sites due to the unique anatomy of acral skin — and because acral melanoma, the dangerous cancer that can arise in these areas, is disproportionately aggressive and frequently diagnosed at advanced stages.

Acral skin, also known as glabrous skin (hairless skin), has a markedly different structure from the hair-bearing skin that covers most of the body. It is characterized by a much thicker epidermis, the presence of distinctive ridges and furrows (dermatoglyphics — fingerprints and footprints), the absence of hair follicles and sebaceous glands, and a higher density of eccrine sweat glands. These anatomical differences profoundly affect how melanocytic lesions appear in these locations, creating patterns that can be misinterpreted by clinicians unfamiliar with acral dermoscopy.

Acral nevi are common, particularly in individuals with darker skin tones — studies have found plantar nevi in up to 20 percent of certain populations. Most are entirely benign, but their clinical importance lies in the need to distinguish them reliably from acral melanoma, which has a worse prognosis than melanoma at other sites partly due to delayed diagnosis.

The distinctive appearance of acral nevi results from the unique architecture of glabrous skin. Unlike hair-bearing skin, where the skin surface is relatively flat and featureless, acral skin is organized into alternating ridges (sulci) and furrows (sulci limitantes) that form the dermatoglyphic patterns we know as fingerprints and footprints. The eccrine sweat ducts open onto the tops of the ridges, while the crista limitans (the anatomic ridge of the dermis) underlies the surface furrow.

This topographic organization means that melanocytes within acral nevi are distributed along these ridges and furrows in specific patterns that have no equivalent on hair-bearing skin. On dermoscopy — the magnified examination technique essential for evaluating pigmented lesions — acral nevi display distinctive patterns not seen on other body sites. The parallel furrow pattern is the most common benign pattern, in which pigmentation follows the furrows (sulci) of the dermatoglyphics, appearing as parallel lines of pigment that align with the skin markings.

Variants include the lattice-like pattern, where pigment lines cross the ridges, and the fibrillar pattern, where thin oblique lines give a striated appearance most commonly seen on weight-bearing areas of the sole. The crista dotted pattern shows pigment dots along the ridges (cristae). These benign patterns reflect the normal distribution of melanocytes within acral skin architecture. Understanding these patterns is essential because the equivalent malignant pattern — the parallel ridge pattern, where pigment follows the ridges rather than the furrows — is the primary dermoscopic indicator of acral melanoma.

Distinguishing benign acral nevi from acral melanoma is one of the most important — and most challenging — tasks in clinical dermatology. Acral melanoma (acral lentiginous melanoma, or ALM) accounts for roughly two to three percent of all melanomas in Caucasian populations but represents a much higher proportion — up to 60 to 70 percent — of melanomas in individuals of African, Asian, and Hispanic descent. This disparity makes acral melanoma a significant health equity issue.

Acral melanoma carries a worse prognosis than melanoma at other sites, largely because of delayed diagnosis — the average Breslow thickness at diagnosis is significantly greater for acral melanoma than for melanoma on sun-exposed skin. Several factors contribute to this delay: palms and soles are not routinely examined during self-skin checks, nail melanoma is frequently mistaken for fungal infection or trauma, darker-skinned individuals may not perceive themselves as at risk for melanoma, and healthcare providers may be less familiar with melanoma in these locations. Clinically, features that should raise concern for acral melanoma include a pigmented lesion larger than seven millimeters on the palm or sole, asymmetric shape, irregular or blurred borders, color variation including brown, black, blue, or red components, and recent change or evolution.

For nail melanoma specifically, Hutchinson's sign — pigment extending from the nail onto the surrounding skin (periungual extension) — is an important warning sign. On dermoscopy, the parallel ridge pattern — where pigment follows the ridges of the dermatoglyphics rather than the furrows — is highly specific for acral melanoma and is the single most important dermoscopic feature to evaluate. Any pigmented acral lesion displaying a parallel ridge pattern should be biopsied promptly.!!

Melanocytic nevi can arise within the nail matrix — the crescent-shaped tissue at the base of the nail from which the nail plate grows — producing a longitudinal band of pigmentation in the nail called melanonychia striata (longitudinal melanonychia). This presents as a brown or brown-black stripe running the length of the nail from the base to the free edge. Longitudinal melanonychia is the clinical presentation that creates the most diagnostic anxiety because it can represent a benign nail nevus, nail melanoma, or several other conditions including ethnic melanonychia (normal pigmentation in darker-skinned individuals), drug-induced pigmentation, fungal infection, or subungual hematoma.

In adults of African descent, longitudinal melanonychia is very common and usually represents normal melanocytic activation — it affects virtually all African American adults by age 50 and multiple nails are typically involved. In Caucasian adults, longitudinal melanonychia is less common and more frequently prompts concern for melanoma. Features suggesting a benign nail nevus include a narrow (under three millimeters), uniform, parallel-bordered band of homogeneous brown color, occurring in a child or young adult, stable over time.

Features raising concern for nail melanoma include a wide (over three millimeters) or widening band, irregular or blurred lateral borders, color heterogeneity within the band (brown, black, gray areas), Hutchinson's sign (periungual pigment extension), nail plate dystrophy (cracking, splitting, thinning), and occurrence in a single digit of an older adult. The thumb, index finger, and great toe are the digits most commonly affected by nail melanoma. Any new or changing longitudinal melanonychia in an adult should be evaluated by a dermatologist experienced in nail dermoscopy.!! Biopsy of the nail matrix is sometimes necessary for definitive diagnosis.

Given the challenges of evaluating pigmented lesions on acral skin, a systematic approach is essential. Clinical assessment begins with noting the location, size, shape, color, border characteristics, and history of the lesion. The ABCDE criteria used for evaluating moles elsewhere apply to acral lesions but with modifications — the threshold for concern should be lower given the higher stakes of delayed diagnosis.

Dermoscopy is indispensable for acral lesion evaluation and requires specific training in acral dermoscopic patterns. The three-step algorithm for acral dermoscopy provides a structured approach: first, determine whether the lesion shows a recognizable benign pattern (parallel furrow, lattice-like, fibrillar, or crista dotted); second, if no benign pattern is identified, check for the parallel ridge pattern (suggestive of melanoma); third, if the pattern is indeterminate, consider biopsy or close follow-up with serial dermoscopy. Biopsy is recommended for any acral lesion with a parallel ridge pattern, any lesion with atypical features that do not fit a recognized benign pattern, any lesion that is changing in size, shape, or color, any pigmented lesion larger than seven millimeters, and any lesion causing clinical concern regardless of dermoscopic findings.

Excisional biopsy is preferred over partial biopsy for accurate histopathologic assessment. For confirmed benign acral nevi, routine monitoring is appropriate with clinical and dermoscopic evaluation at intervals determined by the individual risk profile. Patients should be educated about what to watch for — changes in size, shape, color, or new symptoms — and the importance of including palms, soles, between toes, and nails in self-skin examinations.

Moles on the palms, soles, and nails are among the most anxiety-provoking skin findings because of their association with acral melanoma and the general awareness that melanoma in these locations is often diagnosed late. Skinscanner provides immediate AI-driven analysis when you photograph a pigmented lesion on acral skin, evaluating its visual characteristics including size, shape, border regularity, color homogeneity, and symmetry. The AI has been trained to recognize patterns associated with benign acral nevi and to flag features that raise concern for acral melanoma, helping bridge the gap between noticing a spot and obtaining professional evaluation.

This is particularly valuable because many people do not include their palms, soles, and nails in routine self-skin examinations, and when they do discover a pigmented lesion in these areas, the unusual appearance (compared to moles elsewhere) can cause disproportionate worry. Skinscanner helps provide informed context about acral pigmented lesions, explaining why moles in these locations look different and what features warrant concern versus reassurance. For individuals monitoring existing acral nevi, serial photography through the app enables tracking any changes over time — the single most important factor in identifying a lesion that may be evolving from benign to malignant.

Skinscanner does not replace dermoscopic evaluation by a clinician trained in acral dermoscopy — the distinction between parallel furrow and parallel ridge patterns requires magnified examination beyond standard photography. But for initial assessment and ongoing surveillance, Skinscanner provides an accessible, immediate first step toward proactive acral skin health.