Keratosis Seborrheic: Symptoms, Types, Causes and Treatment

Seborrheic keratosis (SK), often referred to as "keratosis seborrheic," is one of the most common benign skin growths encountered in adults. Despite its prevalence, this skin lesion can be a source of concern due to its varied appearance and, on rare occasions, its resemblance to malignant skin tumors. In this comprehensive guide, we’ll explore the key symptoms, types, causes, and treatment options for seborrheic keratosis, empowering you with current, evidence-based insights into this fascinating dermatological condition.

Symptoms of Keratosis Seborrheic

Seborrheic keratoses are known for their distinctive look and feel, but their variability sometimes makes them difficult to identify. Early recognition is important—not because SKs are dangerous, but to avoid confusion with more serious skin conditions.

Symptom	Appearance	Common Sites	Source(s)
Raised lesion	Waxy, "stuck-on" plaque	Face, trunk	4 5
Color	Tan, brown, black	Face, trunk, limbs	4 5 9
Texture	Verrucous, rough, or smooth	Face, back, neck	4 3
Size	Few millimeters to several centimeters	Face, trunk	4 5

Table 1: Key Symptoms

The Distinctive Look and Feel

SKs commonly appear as slightly raised, waxy plaques that often look as if they were "pasted on" the skin. They may have a wart-like, rough, or even velvety texture. The color spectrum ranges from pale tan to deep brown or black. Over time, these lesions may thicken, and their surface can become more irregular or cracked, sometimes with visible small cysts (milia-like cysts) or comedo-like openings 3 4.

Where Do They Appear?

SKs can occur anywhere except the palms and soles, but they most frequently develop on the face, neck, chest, and back. Sun-exposed areas are especially common sites, possibly due to the influence of ultraviolet radiation 4 6 9. While typically asymptomatic, especially in early stages, some people may experience irritation, itching, or minor bleeding if lesions are scratched or traumatized.

Clinical Variability and Atypical Symptoms

• Pigmentation: Some SKs are so dark they can be mistaken for melanoma.
• Multiplicity: Many adults develop multiple SKs over time.
• Inflammation: Occasionally, lesions can become red or irritated (the irritated subtype), especially due to friction or secondary infection 1.

Key takeaways: SKs are usually benign, recognizable by their unique "stuck-on" appearance and variable color and texture. However, due to their diversity, any sudden change or atypical feature should prompt medical evaluation to rule out malignancy 4 5.

Types of Keratosis Seborrheic

Seborrheic keratoses are not all the same. Both clinicians and pathologists recognize several subtypes, which can differ in appearance, location, and underlying histology. Understanding the main types helps with accurate diagnosis and management.

Type	Description	Common Location/Skin Type	Source(s)
Acanthotic	Thickened, classic appearance	Various	1
Hyperkeratotic	Markedly rough, scaly	Trunk, extremities	1 2
Adenoid	Gland-like pattern in tissue	Sun-exposed areas	1
Melanoacanthoma	Heavily pigmented	Face, trunk	1
Dermatosis papulosa nigra	Small, dark papules	Face (darker skin types)	2 5
Stucco keratosis	Flat, white/gray papules	Lower legs, feet	2
Clonal	Nests of cells in lesion	Various	1
Irritated	Inflamed, often itchy	Friction-prone areas	1
Inverted follicular keratosis	Follicular, wart-like	Face, especially upper lip	2
Lichenoid keratosis	Flat, inflamed, pink to purple	Sun-exposed areas	2 3

Table 2: Main Types of Keratosis Seborrheic

Classic and Histopathological Subtypes

The most common form is the acanthotic type, which features thickened epidermis and is usually seen as the "classic" SK. The hyperkeratotic subtype is characterized by a rough, heavily keratinized surface. Adenoid SKs, more common in sun-exposed areas, display gland-like patterns under the microscope 1.

Pigmented and Ethnic Variants

• Melanoacanthoma: Rich in pigment, these variants can be strikingly dark and are sometimes mistaken for melanoma. Melanoacanthoma variants are more frequent than previously thought, accounting for nearly 10% of cases in some studies 1.
• Dermatosis papulosa nigra (DPN): Common in individuals with darker skin, especially of African descent. DPN presents as multiple small, dark papules on the face and is a benign variant 2 5.

Flat and Stucco Types

• Stucco keratosis: Appears as small, flat, white or gray papules, typically on the lower legs and feet. These are more often seen in older adults 2.
• Flat seborrheic keratosis: These lesions are less raised and may be confused with lentigines or other flat pigmented spots 2.

Special and Rare Forms

• Clonal, irritated, and inverted follicular keratosis are less common but important to recognize, especially if there is inflammation, unusual growth patterns, or suspicion of malignancy 1 2.
• Lichenoid keratosis is a flat, inflamed variant typically found on sun-exposed skin and can resemble other lichenoid dermatoses 2 3.

In summary: The spectrum of SK types is broad, with significant clinical and histological overlap with other skin conditions. Recognizing these variants ensures proper diagnosis and management, especially when atypical features are present 1 2 5.

Causes of Keratosis Seborrheic

Although seborrheic keratoses are extremely common, their exact cause remains partly mysterious. Multiple factors—genetic, environmental, and possibly viral—appear to be involved in their development.

Cause	Mechanism/Details	Evidence	Source(s)
Age	Accumulates with aging	Most common in adults >40	4 5 6
Genetics	Family history, inherited tendency	Familial clustering	4 7 8
Sun Exposure	UV radiation as a trigger	Common on sun-exposed areas	1 6 9
Somatic Mutations	FGFR3, PIK3CA, RAS, AKT1, EGFR	Genetic studies in lesions	5 8
Viral Factors	HPV-like infections suspected	Seen in genital lesions	5 7
Paraneoplastic	Leser–Trélat sign (sudden eruption)	Associated with internal tumors	5

Table 3: Main Causes and Risk Factors

Age and Genetics

The likelihood of developing SK rises sharply with age, with most adults over 40 exhibiting at least one lesion. There is also a well-documented familial predisposition, indicating a genetic basis. Certain families show a clear tendency to develop numerous SKs 4 7 8.

Role of Sun Exposure

Several studies suggest that chronic ultraviolet (UV) radiation may promote the development of SKs, especially on sun-exposed areas such as the face, neck, and hands. The adenoid subtype, in particular, is more frequently found in sun-exposed skin 1 6 9.

Molecular and Cellular Factors

Recent research has identified somatic mutations in genes such as FGFR3, PIK3CA, RAS, AKT1, and EGFR within SK lesions. These mutations are thought to drive the benign proliferation of epidermal cells but do not lead to malignant transformation, distinguishing SK from cancerous tumors 5 8.

Possible Viral Involvement

HPV-like viral particles have occasionally been detected in genital SKs, but their causative role is still debated. The resemblance of SK to common warts (verruca vulgaris) and rare reports of linear or grouped lesions have led to speculation about possible viral etiology, but clear evidence is lacking 5 7.

Paraneoplastic Syndromes

A sudden eruption of multiple SKs—known as the Leser–Trélat sign—can sometimes be a cutaneous marker for internal malignancy, most often gastrointestinal cancers. However, this is rare, and most SKs are not associated with internal disease 5.

Bottom line: SKs result from a complex interplay of age, genetics, environmental factors, and somatic mutations. While usually benign, their sudden appearance or atypical features should prompt further medical evaluation 4 5 8.

Treatment of Keratosis Seborrheic

Although seborrheic keratoses are harmless, many people choose to remove them for cosmetic reasons or due to irritation. A wide range of treatment options is available, each with specific benefits and drawbacks.

Treatment	Method/Approach	Outcomes/Considerations	Source(s)
Cryotherapy	Liquid nitrogen freezing	Effective, but less satisfaction	10 12
Electrosurgery	Burning/cauterization	High efficacy, scarring risk	10 12
Laser Therapy	CO2, Er:YAG, Copper Vapour	Excellent outcomes, minimal scars	10 11
Shave Excision	Physical removal	Quick, may recur	4 5
Topical Therapy	40% hydrogen peroxide, nitric-zinc	Promising for facial lesions	5 12
No Treatment	Watchful waiting	Benign, no risk if unchanged	4 5

Table 4: Main Treatment Options for Seborrheic Keratosis

Traditional Surgical Options

• Cryotherapy: Involves freezing the lesion with liquid nitrogen. It is effective but can lead to hypopigmentation, especially in people with darker skin, and has lower patient satisfaction compared to other methods 10 12.
• Electrosurgery (Electrodesiccation): Uses electric current to destroy the lesion. This method offers high efficacy but carries a risk of post-treatment scarring and pigment changes 10 12.
• Shave Excision: Simple removal with a surgical blade. It is quick and effective for raised lesions but may not prevent recurrence or address deeper tissue 4 5.

Laser-Based Techniques

• CO2 and Er:YAG Lasers: These lasers vaporize SKs with precision, resulting in excellent cosmetic outcomes and minimal scarring. Patient satisfaction is generally high, though Er:YAG laser treatment may result in slightly more prolonged redness 10.
• Copper Vapour Laser (CVL): Recent studies suggest that CVL is both safe and effective, with minimal side effects and optimal cosmetic results 11.

Emerging and Non-Invasive Therapies

• Topical 40% Hydrogen Peroxide (HP40): Recently approved for use, HP40 offers a non-surgical option, especially for facial SKs. Early studies show promising efficacy with minimal side effects 5 12.
• Aqueous Nitric-Zinc Complex: Another topical option under investigation, with early results showing efficacy for select lesions 5.

When to Treat—and When Not To

• No Treatment Needed: Most SKs do not require removal unless they are symptomatic or cause cosmetic concern 4 5.
• Biopsy: Any lesion with atypical features or rapid change in appearance should be biopsied to rule out malignancy, especially those on sun-exposed skin 1.

Special Considerations

• Cosmetic outcomes are increasingly important, especially in patients with darker skin types who are at greater risk for pigmentary changes after procedures 12.
• Treatment choice should be individualized, taking into account patient preference, lesion location, skin type, and risk of scarring or pigment alteration 4 5 12.

Conclusion

Seborrheic keratosis is a common, benign skin growth with a remarkable range of clinical presentations. While usually harmless, it is important to distinguish SK from malignant lesions and to offer individualized treatment options when removal is desired.

Main Points Covered:

• Symptoms: SKs are typically "stuck-on," waxy, and vary in color and size. They occur mostly on sun-exposed areas, especially in older adults 4 5.
• Types: There are many subtypes, including acanthotic, hyperkeratotic, adenoid, melanoacanthoma, dermatosis papulosa nigra, and others, each with distinctive features 1 2 5.
• Causes: Multiple factors contribute, including age, genetics, sun exposure, and somatic mutations. Sudden eruptions may rarely signal internal malignancy 4 5 8.
• Treatment: Options include cryotherapy, electrosurgery, various laser therapies, and new topical agents. Treatment is often chosen for cosmetic reasons, and should be tailored to the individual 10 11 12.

If you notice any new, changing, or unusual skin lesions, especially those with rapid growth, irregular pigmentation, or bleeding, consult a dermatologist for proper evaluation. Most SKs are harmless, but vigilance ensures peace of mind and optimal skin health.