Nevus: Symptoms, Types, Causes and Treatment

Nevus (plural: nevi), commonly known as moles or birthmarks, are among the most common skin findings in humans. While most nevi are harmless and primarily a cosmetic concern, some can be associated with syndromes, functional impairments, or even malignancy risk. Understanding the symptoms, types, causes, and treatment options for nevi is crucial for both patients and healthcare providers. This article provides an evidence-based overview of nevi, synthesizing the latest research to answer common questions and guide informed decisions.

Symptoms of Nevus

Nevi may appear at birth or develop later in life, and their clinical presentation can range from subtle pigmented macules to raised, hairy, or verrucous plaques. Recognizing the key symptoms helps distinguish benign nevi from those requiring further evaluation or intervention.

Symptom	Description	Significance	Source(s)
Pigmentation	Tan, brown, black, or bluish coloration	Most common presentation	4 6 7 9 11
Texture	Smooth, verrucous, or rough surface	Helps subtype identification	4 6 10
Hair Growth	Increased hairiness over lesion	Becker nevus, others	6
Size/Shape	Variable; can be small macules or large plaques	Diagnostic clues	2 4 8 9
Associated Symptoms	Pain, pruritus, tumors in some syndromes	Suggests complications	2 8
Systemic Involvement	Neurologic, skeletal, ocular changes	Indicates syndromic nevus	1 2 5 6

Table 1: Key Symptoms

Pigmentation and Appearance

Nevi typically present as well-demarcated pigmented lesions. Colors may range from tan or light brown in Becker's nevus to bluish in nevus of Ota, or dark brown/black in melanocytic nevi. Some nevi, like Hori’s nevus, manifest as gray-blue macules, especially on the face of middle-aged women 9 11.

Texture and Surface Changes

The surface of a nevus varies by type. Epidermal nevi may be verrucous (wart-like), smooth, or rough. Nevus comedonicus often presents as grouped or linear comedone-like plugs, while sebaceous nevus is usually smooth at birth but becomes more irregular and thickened at puberty 2 4 10.

Hair Growth

Certain nevi, most notably Becker's nevus, are associated with increased hair growth (hypertrichosis), especially in males after puberty. Not all nevi will have this feature, and it is less common in females 6.

Size, Shape, and Distribution

Nevi can be solitary or multiple, small or large, and may follow linear or segmental distributions, especially in syndromic cases. Giant congenital melanocytic nevi can cover large body areas and often have irregular or “archipelago” borders 8.

Associated Symptoms and Systemic Involvement

Some nevi, especially those that are part of a syndrome, are associated with pruritus, pain, or tumor formation (benign or rarely malignant). Systemic involvement may include neurologic deficits, ocular changes, or skeletal abnormalities, alerting clinicians to possible syndromic forms such as Schimmelpenning syndrome or Becker nevus syndrome 1 2 5 6 8.

Types of Nevus

Nevi are a heterogeneous group, encompassing multiple subtypes with distinct clinical and histological features. Accurate classification is essential for risk assessment and management.

Type	Key Features	Risk/Implication	Source(s)
Melanocytic Nevus	Pigmented, can be congenital or acquired	Rare malignancy risk	3 7 8
Epidermal Nevus	Verrucous, linear, often present at birth	May be syndromic	1 4
Sebaceous Nevus	Yellowish, smooth at birth, thickens at puberty	Tumor risk with age	2 4 6
Becker's Nevus	Tan patch, hypertrichosis, adolescent onset	Becker nevus syndrome	6
Nevus Comedonicus	Comedone-like plugs, linear/grouped	Rare systemic effects	5 10
Nevus of Ota	Blue/gray facial patch, usually unilateral	Ocular/psychosocial	9
Hori's Nevus	Bilateral facial macules, middle-aged onset	Cosmetic concern	11

Table 2: Major Types of Nevus

Melanocytic Nevi

These are the classic "moles," composed of melanocyte clusters. They may be congenital or acquired and vary in size. Giant congenital melanocytic nevi carry a small but significant risk for melanoma and may be associated with neurocutaneous melanocytosis 3 8.

Epidermal Nevi

Epidermal nevi are hamartomatous overgrowths of the epidermis, often following Blaschko's lines. They are classified into types such as verrucous epidermal nevus, nevus comedonicus, and Becker's nevus. Syndromic forms, where skin lesions are associated with neurologic, ocular, or skeletal anomalies, are recognized 1 4 5 6.

Sebaceous Nevus

Commonly found on the scalp or face, these lesions are smooth and yellowish at birth, becoming more irregular and thickened during puberty. In adulthood, sebaceous nevi can give rise to benign (and rarely malignant) tumors 2.

Becker's Nevus

Typically appearing in adolescence as a unilateral tan patch with increased hair growth, Becker's nevus may be associated with musculoskeletal anomalies and breast hypoplasia in "Becker nevus syndrome" 6. It is androgen-dependent and affects males and females equally.

Nevus Comedonicus

This rare type features grouped or linear comedone-like plugs. Nevus comedonicus syndrome includes associations with congenital cataracts, skeletal malformations, and sometimes neurologic anomalies 5 10.

Nevus of Ota and Hori's Nevus

Nevus of Ota is characterized by bluish or gray-brown discoloration on the face, frequently involving the sclera, and is most common in Asian populations. Hori’s nevus presents as bilateral blue-brown macules on the face, usually in middle-aged women 9 11.

Causes of Nevus

Understanding what leads to the formation of nevi is crucial for both prevention (when possible) and for genetic counseling in syndromic cases. The etiology is complex, involving genetic, developmental, and sometimes environmental factors.

Cause	Mechanism/Detail	Relevance	Source(s)
Genetic Mutation	Postzygotic somatic mutations (e.g., ACTB, HRAS, KRAS, NEK9, FGFR3)	Drives many nevi types	1 5 6 8
Developmental Mosaicism	Mutation occurs after fertilization	Explains segmental/linear patterns	1 5 6
Hormonal Influence	Androgen-dependent (e.g., Becker’s nevus)	Explains puberty onset	6
Environmental	UV exposure, trauma (minor factors)	May influence appearance	7
Traditional Medicine	Humoral imbalance (black bile)	Historical perspective	7

Table 3: Main Causes of Nevus

Genetic Mutations and Mosaicism

Most nevi, especially complex or syndromic forms, arise from postzygotic (after fertilization) somatic mutations. These mutations affect genes such as ACTB (Becker's nevus), HRAS/KRAS (Schimmelpenning syndrome), NEK9 (nevus comedonicus), and FGFR3 (epidermal nevus syndrome) 1 5 6. The timing and distribution of mutated cells during early development determine the pattern and extent of the nevus, often resulting in mosaicism.

Hormonal Factors

Certain nevi, like Becker's nevus, are androgen-dependent, typically appearing or becoming more prominent during puberty. This hormonal influence may explain the timing and some of the clinical features, such as increased hair growth 6.

Environmental and Other Factors

While genetics play the central role, environmental factors like UV radiation may induce or darken some acquired melanocytic nevi. Traditional perspectives, such as those from Iranian medicine, attribute nevi to imbalances in bodily fluids (humors), specifically black bile, but there is no scientific evidence supporting this theory 7.

Syndromic Associations

Some nevi are part of broader syndromes that include neurologic, skeletal, or ocular anomalies. These are due to the widespread distribution of mutated cells affecting multiple tissue types 1 5 6.

Treatment of Nevus

Treatment of nevi depends on their type, size, location, associated symptoms, and potential for malignancy or syndromic involvement. Most nevi are benign and require no intervention unless for cosmetic or functional reasons; however, certain types and complications warrant active management.

Treatment	Indication/Use	Advantages/Limitations	Source(s)
Surgical Excision	Large, symptomatic, or suspicious nevi	Complete removal; scarring risk	2 4 10 12
Laser Therapy	Pigmented nevi, nevus of Ota, Hori's nevus	Cosmetic improvement, less invasive	4 9 11
Topical/Medical	Retinoids for comedonicus, MEK inhibitors for melanocytic nevi	Symptom relief; limited efficacy	8 10
Dermabrasion	Superficial nevi, comedonicus	Cosmetic result; recurrence risk	10 11
Observation	Asymptomatic, benign-appearing nevi	No risk; regular monitoring	2 4
Non-physician Removal	Plasma pen, cryo/radiofrequency cautery	Widely used, but safety concerns	12

Table 4: Treatment Approaches

Surgical Excision

Surgical removal is indicated for nevi with suspicious changes, symptomatic lesions (pain, pruritus, recurrent infections), or those at risk for malignancy (e.g., giant congenital melanocytic nevus). Surgery is also considered for cosmetic reasons, though scarring may occur, especially with larger lesions 2 4 10 12.

Laser Therapy

Lasers are the first-line therapy for pigmented nevi like nevus of Ota and Hori’s nevus. Q-switched Nd:YAG and picosecond-domain lasers are effective, particularly when started early in life (before age 5), resulting in better pigment clearance and lower risk of complications such as postinflammatory hyperpigmentation 9 11. Laser therapy is also used for some epidermal nevi, with variable success 4.

Topical and Medical Treatments

Topical retinoids and keratolytics are sometimes used for nevus comedonicus, though their efficacy is limited. For giant congenital melanocytic nevi with specific genetic mutations (e.g., BRAF fusion), targeted therapies such as MEK inhibitors (e.g., trametinib) have shown promise in individual cases, especially for symptom relief 8 10.

Dermabrasion and Other Procedures

Dermabrasion and manual extraction are used for superficial or comedonic nevi, but recurrence is possible. Newer approaches, such as diode laser, are being explored for certain types 10 11.

Observation and Monitoring

Most benign nevi, especially if asymptomatic and not cosmetically concerning, are best managed with observation and regular follow-up to monitor for changes suggestive of malignancy or complications 2 4.

Caution with Non-Physician Removal

Non-physician cosmetic practitioners often use plasma pens, cryotherapy, and cautery devices for mole removal. While these are popular, especially on social media, they can carry risks of scarring, incomplete removal, or incorrect diagnosis, underscoring the importance of physician oversight 12.

Conclusion

Nevi represent a diverse group of skin lesions, ranging from harmless moles to complex syndromic disorders. While most require no treatment, accurate recognition, risk assessment, and individualized management are vital.

Key Points:

• Nevi can present with varied symptoms, including pigmentation changes, texture alterations, hair growth, and sometimes pain or systemic involvement.
• Types include melanocytic, epidermal, sebaceous, Becker’s, comedonicus, and special forms like nevus of Ota and Hori’s nevus.
• Genetic mutations and developmental mosaicism are the primary causes, with some nevi linked to hormonal factors or syndromic associations.
• Treatment depends on type, symptoms, and risk; options include surgery, laser, topical/medical therapy, and observation, with physician oversight critical for safety and efficacy.

Understanding nevi empowers individuals to seek appropriate care and helps clinicians provide the best possible outcomes for their patients.