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What is Seborrheic Keratosis?
Seborrheic keratosis is one of the most common benign skin growths seen in adults, particularly in individuals over the age of 40. Also known as a seborrheic wart or verruca seborrhoica, it appears as a raised lesion on the skin surface with a rough, wart-like texture and a color that ranges from light brown to deep black. Despite its sometimes alarming appearance, seborrheic keratosis is entirely benign and, in the vast majority of cases, requires no medical treatment whatsoever.
These skin growths are extremely prevalent in the general population. Studies suggest that nearly all people will develop at least one seborrheic keratosis during their lifetime, with the incidence increasing significantly with age. It is not uncommon for older adults to present with dozens, or even hundreds, of these lesions distributed across different parts of the body.
While seborrheic keratoses are harmless from a medical standpoint, they can sometimes resemble more serious skin conditions, including certain forms of skin cancer. This is why awareness, accurate diagnosis, and regular dermatological check-ups are essential tools for maintaining skin health and peace of mind. Understanding what seborrheic keratosis is, what it looks like, and when to seek medical advice can make a significant difference in patient outcomes. This is not because of the lesion itself but because it is important to rule out malignant conditions.
Causes
Despite being such a common condition, the exact cause of seborrheic keratosis remains unknown. This is one of the more intriguing aspects of this skin condition: it is extremely widespread, yet science has not definitively identified a single triggering factor.
The Role of Keratinocytes
From a histological standpoint, meaning when examining tissue under a microscope, seborrheic keratosis involves a proliferation of keratinocytes. These are the cells that make up the outermost layer of the skin, known as the epidermis. More specifically, there is a thickening of the cells in the stratum corneum, which is the most superficial portion of the epidermis. This layer is composed of cells called corneocytes, which have already lost their nuclei as part of the natural skin maturation process.
What triggers this abnormal thickening and proliferation is not fully understood. Researchers have explored several potential contributing factors over the years, but none have been conclusively proven as primary causes in all cases.
Ultraviolet (UV) Radiation
One hypothesis is that prolonged exposure to ultraviolet radiation from the sun may contribute to the development of seborrheic keratoses. However, the evidence linking UV exposure directly to the number or severity of lesions is not definitive. Interestingly, seborrheic keratoses also appear in areas of the body that are not typically exposed to sunlight, which suggests that UV radiation alone cannot account for the condition.
Genetic Predisposition
A genetic predisposition is considered likely by many dermatologists. It is commonly observed that seborrheic keratoses run in families, and individuals with a family history of the condition are more likely to develop a significant number of lesions. The specific genetic mechanisms involved have not yet been fully characterized. However, certain mutations in genes related to cell signaling pathways, particularly the FGFR3 (fibroblast growth factor receptor 3) and PIK3CA genes, have been identified in some seborrheic keratoses. This suggests a possible genetic component at the cellular level.
The Sign of Leser-Trelat: When Seborrheic Keratosis May Signal Something More Serious
A particularly important concept for both patients and clinicians is the Sign of Leser-Trelat. This refers to the sudden and rapid appearance of multiple seborrheic keratoses. This phenomenon, known as eruptive seborrheic keratoses, may in some cases serve as a paraneoplastic sign. In other words, the sudden eruption of numerous seborrheic keratoses across the body could potentially be associated with an internal malignancy, such as gastrointestinal cancers (particularly adenocarcinoma of the stomach), lymphomas, or other systemic malignancies.
The underlying mechanism is thought to involve the circulation of growth factors released by the tumor, which stimulate the abnormal proliferation of keratinocytes. It is important to emphasize that isolated or gradually appearing seborrheic keratoses are not linked to internal cancer. The concern arises specifically when many lesions appear suddenly and at the same time. In such cases, a thorough medical evaluation is strongly recommended.
Are Seborrheic Keratoses Contagious?
A common misconception is that seborrheic keratoses are related to viral warts and might therefore be contagious. This is not the case. Although seborrheic keratoses may sometimes resemble viral warts in appearance, they have no infectious cause and are not contagious. They cannot be transmitted from person to person through direct or indirect contact. The similarities in appearance are purely coincidental. They result from comparable superficial skin changes, not a shared cause.
Clinical Manifestations and Symptoms
Seborrheic keratoses have a characteristic clinical appearance that, to an experienced dermatologist, is usually immediately recognizable. However, because they can vary considerably in color, size, shape, and surface texture, understanding their typical features is essential for both patients and healthcare professionals.
How Seborrheic Keratoses Develop
Seborrheic keratoses typically follow a gradual developmental progression:
- They begin as flat lesions, called macules, which are subtle discolorations on the skin surface without elevation or texture change.
- Over time, they progressively thicken and become raised, evolving into:
- Papules: raised lesions smaller than 1 centimeter in diameter.
- Plaques: raised lesions larger than 1 centimeter, often resulting from the merging (confluence) of multiple papules.
Once a seborrheic keratosis reaches the plaque or papule stage, it may remain essentially unchanged for the rest of a person’s life unless it is physically removed or subjected to trauma or irritation.
Surface Characteristics
One of the most distinctive features of seborrheic keratoses is their superficial quality. These lesions appear to “sit on top” of the skin rather than growing into it. They do not infiltrate the deeper layers of the skin, which is one reason why they are considered benign.
The surface is characteristically warty and rough, covered with greasy or waxy scales. The outermost layer is loosely adherent to the underlying skin, to the point that it can sometimes be scratched off with a fingernail or gently removed with a curette (a round-bladed surgical instrument). This quality of being easily dislodged is sometimes a helpful diagnostic clue, although it should not be used as a self-diagnostic technique by patients.
Color Variations
The color of seborrheic keratoses can vary widely:
- Light yellow to tan in early lesions
- Medium brown to dark brown in more developed lesions
- Dark brown to black in advanced or heavily pigmented lesions
When a seborrheic keratosis is very dark or black, it may be referred to clinically as a melanoacanthoma. This variant is histologically characterized not only by the typical keratinocyte proliferation but also by a significant increase in melanocytes (the cells responsible for skin pigmentation). Melanoacanthomas can be particularly challenging to differentiate from melanoma without dermatoscopic evaluation.
Number, Shape, and Distribution
Seborrheic keratoses are often multiple, ranging from just a few lesions to hundreds. Their shape can be:
- Round
- Oval
- Irregular
When lesions are numerous, they may be distributed randomly across the skin surface, or they may follow a linear arrangement along skin folds or the directions of clothing friction. For example, lesions may align along the inframammary folds (the skin creases beneath the breasts) in women.
Preferred Body Locations
The term “seborrheic” in the name refers to the characteristic distribution of these lesions. This distribution tends to correspond to seborrheic areas of the body, which are regions with a high density of sebaceous (oil-producing) glands.
- Face (especially the forehead, temples, and cheeks)
- Chest (particularly the sternal region)
- Back (upper and mid-back)
- Abdomen
- Axillary folds (armpits)
- Inguinal folds (groin area)
On the lower limbs, lesions are less common. When they do appear on the legs, they often present as multiple small, grayish lesions known as stucco keratoses. This is a specific variant of seborrheic keratosis, characterized by a distinctive chalky, stuck-on appearance.
Symptoms
In the majority of cases, seborrheic keratoses are asymptomatic, meaning they cause no pain, itching, or discomfort. However, depending on their location and size, some patients may experience:
- Itching or irritation, particularly in areas where the lesion rubs against clothing or jewelry
- Tenderness or discomfort if the lesion is located in a skin fold or on a pressure point
- Cosmetic concerns, especially when lesions appear on visible areas like the face or neck
It is worth noting that any change in a seborrheic keratosis, such as sudden growth, increased pigmentation, bleeding, or soreness, should be evaluated by a dermatologist promptly. This is not because the lesion itself is likely to become malignant; rather, such changes may indicate a different diagnosis altogether.
Diagnosis
The diagnosis of seborrheic keratosis is primarily a clinical diagnosis, meaning it is usually made by a dermatologist through direct visual examination of the lesion. In most cases, an experienced dermatologist can identify a seborrheic keratosis at a glance without the need for invasive procedures.
Dermoscopy
The clinical examination is often supported by dermoscopy (also called dermatoscopy or epiluminescence microscopy). This is a non-invasive diagnostic technique that uses a handheld device called a dermatoscope, which illuminates the skin and magnifies it tenfold (×10). Dermoscopy allows the clinician to visualize the morphological characteristics of the superficial skin layers and skin lesions that would otherwise be invisible to the naked eye.
Key dermoscopic features of seborrheic keratosis include:
- Milia-like cysts: small, white or yellowish, round structures within the lesion
- Comedo-like openings: dark, round or oval plugged follicles resembling comedones (blackheads)
- Fissures and ridges: a cerebriform (brain-like) surface pattern
- Hairpin vessels: looped blood vessels at the periphery
- Sharp demarcation: clear, well-defined borders separating the lesion from surrounding normal skin
These dermoscopic features help differentiate seborrheic keratosis from other pigmented skin lesions, particularly malignant ones.
Differential Diagnosis: Conditions to Rule Out
The most important clinical challenge is distinguishing seborrheic keratosis from malignant skin lesions, some of which can mimic its appearance closely. The following conditions must be considered in the differential diagnosis:
Malignant Conditions
-
Superficial spreading melanoma: presents as a flat, solitary lesion with irregularly distributed pigment and asymmetrical, irregular borders. Unlike seborrheic keratosis, the color variation within the lesion is often marked, with shades of brown, black, pink, and even white or blue.
-
Nodular melanoma: a raised, dark-colored lesion that may bleed in advanced stages. Its rapid growth and deep pigmentation can superficially resemble a very dark seborrheic keratosis.
-
Pigmented basal cell carcinoma: typically a flat, irregularly shaped lesion with a raised, pearly peripheral rim. The surface may show translucency and fine telangiectasias (dilated blood vessels).
-
Squamous cell carcinoma: sometimes presents as a thick, warty, crusted lesion that may bleed. Unlike seborrheic keratosis, squamous cell carcinoma tends to infiltrate the deeper skin layers and can arise from pre-existing actinic keratoses.
Benign Conditions
Seborrheic keratosis should also be distinguished from other benign skin conditions:
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Solar lentigo (age spot): a flat, non-palpable brown macule resulting from UV-induced melanocyte proliferation. Unlike seborrheic keratosis, it has no raised component.
-
Melanocytic nevus (mole): has a smooth, non-scaly surface, in contrast to the rough, warty texture of seborrheic keratosis.
-
Pigmented actinic keratosis: a rarer variant that affects the face and has a drier surface than seborrheic keratosis. Importantly, actinic keratosis is a pre-malignant lesion that, if left untreated, can progress to squamous cell carcinoma over a variable period of time.
When is a Biopsy Necessary?
In the vast majority of cases, biopsy is not needed to diagnose seborrheic keratosis. However, surgical excision with histological examination is recommended when:
- There is clinical or dermoscopic uncertainty about the nature of the lesion
- The lesion shows atypical features suggestive of malignancy
- The lesion has changed rapidly in size, color, or morphology
- The patient presents with the Sign of Leser-Trelat (sudden eruption of multiple lesions)
In these cases, the excised tissue is sent to a pathology laboratory, where a specialist examines it under a microscope to confirm or rule out malignancy. This is the gold standard for definitive diagnosis when clinical uncertainty exists.
Prognosis and Complications
The natural history and prognosis of seborrheic keratosis are entirely benign. These lesions do not have the capacity to transform into skin cancer on their own. Over time, seborrheic keratoses tend to:
- Increase in number: new lesions may continue to appear with advancing age
- Enlarge gradually: existing lesions may slowly grow larger
- Occasionally shed spontaneously: some lesions may detach on their own, particularly following minor trauma
Irritated or Inflamed Seborrheic Keratosis
The most common complication of seborrheic keratosis is irritation or inflammation, which can be triggered by:
- Mechanical friction from clothing, belts, bra straps, or other fabrics
- Scratching or picking at the lesion
- Chemical irritants such as certain cosmetics or skincare products
- Accidental trauma during daily activities
When a seborrheic keratosis becomes irritated or inflamed, it may exhibit the following changes:
- Increased size due to local edema (swelling)
- Redness and warmth around and within the lesion
- Bleeding from the surface, which can be alarming but is usually minor
- Crusting or oozing from the disrupted surface
These changes can make an inflamed seborrheic keratosis difficult to distinguish clinically from a malignant lesion, which is why any significantly changed or bleeding lesion should be evaluated by a dermatologist as soon as possible. In many cases, inflamed seborrheic keratoses are removed for diagnostic certainty and patient comfort.
Psychological Impact
While seborrheic keratoses are medically harmless, they can have a significant psychological and emotional impact, particularly when they appear on highly visible areas of the body such as the face, neck, or décolletage. Patients may experience:
- Self-consciousness or embarrassment about their appearance
- Anxiety about the nature of the lesion, particularly when it resembles a mole or wart
- Social withdrawal or avoidance of activities such as swimming that require skin exposure
These concerns are entirely valid and should be taken seriously by healthcare providers. Cosmetic treatment options are available and can be discussed with a dermatologist.
Remedies and Treatment
As a benign condition, seborrheic keratosis does not require treatment from a medical necessity standpoint. However, treatment is often sought for cosmetic reasons, for the relief of physical discomfort caused by irritation, or when there is diagnostic uncertainty.
Several effective treatment options are available, ranging from topical therapies to minor surgical procedures. The choice of treatment depends on the size, location, and number of lesions, as well as the patient’s preferences and overall health status.
Topical Keratolytic Agents
Keratolytic creams work by breaking down the bonds between skin cells in the outer layer of the skin, effectively dissolving and loosening the thickened keratinous material that makes up the seborrheic keratosis. The most commonly used keratolytic agent for this purpose is urea, typically in concentrations of 40–50%.
When using keratolytic creams:
- The cream should be applied only to the lesion itself, carefully avoiding the surrounding healthy skin, which could be irritated or damaged by the high concentration of active ingredient
- Treatment typically requires repeated applications over several weeks
- Results can be variable, and complete removal may not always be achieved
Other keratolytic agents that may be used include salicylic acid and alpha-hydroxy acids, although these are generally less potent than high-concentration urea formulations.
Cryotherapy with Liquid Nitrogen
Cryotherapy is one of the most widely used and effective treatments for seborrheic keratosis. It involves the application of liquid nitrogen (at a temperature of approximately −196°C) directly to the lesion using a spray device or a cotton-tipped applicator.
The extreme cold causes rapid freezing and thawing of the cellular water within the lesion, leading to cell death and destruction of the abnormal tissue. The treated area typically:
- Develops a blister or crust within 24–48 hours
- The crust dries and falls off within 1–2 weeks
- Normal skin gradually regenerates underneath
Cryotherapy is quick, generally well-tolerated, and does not usually require anesthesia. However, it may cause:
- Temporary pain or stinging during and after application.
- Hypopigmentation (lightening of the skin) or, less commonly, hyperpigmentation at the treated site may occur. This can be a concern in patients with darker skin tones.
- Incomplete removal requiring a second treatment session.
Diathermocoagulation (Electrocautery)
Diathermocoagulation, also known as electrocautery or electrosurgery, uses high-frequency electrical current to generate heat, which is applied to the seborrheic keratosis to destroy its tissue. This technique is precise and effective, and is particularly useful for larger or thicker lesions.
The procedure is typically performed under local anesthesia and is well-tolerated by most patients. After treatment, the area heals over 1–2 weeks. As with cryotherapy, there is a risk of post-inflammatory pigmentary changes, particularly in individuals with darker skin.
Curettage
Curettage involves physically scraping away the seborrheic keratosis with a curette, a small surgical instrument shaped like a spoon. This tool has either a sharp or semi-sharp edge. Because seborrheic keratoses are superficial and loosely adherent to the underlying skin, they can often be removed relatively easily with a curette.
Curettage is frequently combined with electrodesiccation (drying of tissue with electrical current) to address any residual tissue and minimize bleeding. The procedure is usually performed under local anesthesia. It heals well, although scarring is possible if the technique is not executed carefully.
Surgical Excision
Surgical excision, which involves completely removing the lesion under local anesthesia, is generally reserved for cases where there is diagnostic uncertainty. When a dermatologist cannot confidently distinguish a seborrheic keratosis from a malignant lesion by clinical and dermoscopic examination alone, the entire lesion is surgically removed and sent for histological analysis (examination under a microscope by a pathologist).
This is the most definitive diagnostic method and also provides complete removal of the lesion in a single procedure. The main disadvantage is the potential for scarring, which can be significant depending on the size and location of the lesion.
Newer and Emerging Treatments
Research into non-invasive treatments for seborrheic keratosis is ongoing. Among the more recent developments:
- Hydrogen peroxide (H₂O₂) 40% topical solution: A topical solution of hydrogen peroxide at 40% concentration (brand name Eskata in the United States) has been approved by the FDA for the treatment of seborrheic keratoses. It is applied in-office by a healthcare professional and has shown efficacy in clinical trials for reducing the appearance of seborrheic keratoses.
- Laser therapy: Various laser modalities, including CO₂ laser and erbium YAG laser, have been used for the treatment of seborrheic keratoses, with good cosmetic results. These are typically used in aesthetic dermatology settings.
Post-Treatment Care
Regardless of the treatment method chosen, post-treatment care is important for optimal healing and cosmetic outcomes:
- Keep the treated area clean and dry during the initial healing phase
- Avoid picking or scratching any crusts or scabs that form
- Apply sunscreen to the treated area once it has healed to minimize the risk of post-inflammatory hyperpigmentation
- Follow up with your dermatologist if the lesion does not appear to heal normally or if new lesions develop
Prevention
Unfortunately, there are no proven preventive measures that can reliably prevent the development of seborrheic keratoses. Because the exact cause of the condition is unknown and a genetic predisposition is likely involved, targeted prevention is not currently possible.
Can Sun Protection Help?
While the direct link between UV exposure and seborrheic keratosis is not definitively established, general sun protection practices are always recommended for overall skin health. These include:
- Daily use of broad-spectrum SPF 30+ sunscreen on exposed skin
- Wearing protective clothing, hats, and sunglasses
- Avoiding peak sun exposure hours (typically 10 AM to 4 PM)
- Seeking shade whenever possible
These measures may not prevent seborrheic keratoses specifically, but they significantly reduce the risk of other skin conditions, including melanoma, squamous cell carcinoma, basal cell carcinoma, and solar lentigines.
Monitoring Your Skin
The single most important step patients can take is to monitor their skin regularly and seek dermatological evaluation when they notice new or changing lesions. This is not a preventive measure against seborrheic keratosis per se, but it is essential for early detection of any skin lesions that could be malignant.
Recommended practices include:
- Performing a monthly self-examination of the skin in good lighting, using a mirror to check difficult-to-see areas.
- Scheduling annual or biannual dermatological check-ups, particularly for individuals over 40, those with a family history of skin cancer, or those with fair skin.
- Using the ABCDE rule as a guide: Asymmetry, Border irregularity, Color variation, Diameter greater than 6mm, and Evolution (change). Any of these features in a skin lesion warrants medical evaluation.
Lifestyle Considerations
While lifestyle changes cannot prevent seborrheic keratoses, maintaining overall skin health through the following measures is always beneficial:
- Staying well-hydrated to support skin barrier function
- Eating a balanced diet rich in antioxidants (fruits, vegetables, whole grains) to support cellular health
- Avoiding smoking, which impairs skin circulation and accelerates aging
- Managing stress, which can negatively impact skin health through hormonal pathways
- Using gentle, non-irritating skincare products to minimize trauma to existing lesions
Frequently Asked Questions
Are seborrheic keratoses dangerous?
No. Seborrheic keratoses are entirely benign and have no potential to become cancerous on their own. However, because they can sometimes resemble malignant lesions, it is important to have any new or changing skin growth evaluated by a dermatologist.
At what age do seborrheic keratoses typically appear?
Seborrheic keratoses most commonly begin to appear after the age of 40, though they can occasionally develop in younger adults. Their prevalence and number tend to increase with age.
Can I remove a seborrheic keratosis at home?
It is strongly advised not to attempt home removal of seborrheic keratoses. Picking, scratching, or trying to remove them without professional guidance can lead to infection, scarring, bleeding, and, more importantly, may prevent an accurate professional diagnosis of the lesion.
Will seborrheic keratoses come back after treatment?
Treatment effectively removes individual lesions, but it does not prevent new ones from forming in other locations. Patients with a tendency to develop many seborrheic keratoses will likely continue to see new lesions appear over time.
Do seborrheic keratoses need to be removed?
Medically speaking, no. Seborrheic keratoses are harmless and do not need to be removed unless they are causing discomfort, cosmetic concern, or unless there is diagnostic uncertainty that warrants excision for histological analysis.
Can seborrheic keratoses itch?
Yes. While many seborrheic keratoses cause no symptoms, some may become itchy. This is especially true if they are located in areas prone to friction or if they become inflamed. A new or worsening itch from a skin lesion should always be evaluated by a dermatologist.
Is there a link between seborrheic keratosis and skin cancer?
Seborrheic keratoses themselves are not cancerous and do not increase the risk of skin cancer. The main concern is the possibility of misdiagnosis: a melanoma or other skin cancer could be mistaken for a seborrheic keratosis, or vice versa. This underscores the importance of professional evaluation for any new or changing skin lesion.
Sources and Bibliography
- Cainelli T., Giannetti A., Rebora A. Manuale di dermatologia medica e chirurgica. McGraw-Hill, 4th edition.
- Saurat J., Grosshans E., Laugier P., Lachapelle J. Dermatologia e malattie sessualmente trasmesse. Italian edition edited by Girolomoni G. and Giannetti A. Third edition, 2006. Masson.
- Hafner C., Vogt T. “Seborrheic keratosis”. Journal der Deutschen Dermatologischen Gesellschaft. 2008;6(8):664-677.
- Gill D., Dorevitch A., Marks R. “The prevalence of seborrheic keratoses in people aged 15 to 30 years”. Archives of Dermatology. 2000;136(6):759-762.
- Braun R.P., et al. “Dermoscopy of pigmented seborrheic keratosis”. Archives of Dermatology. 2002;138(12):1556-1560.
- Kasper D.L., et al. Harrison’s Principles of Internal Medicine. 20th edition. McGraw-Hill Education.
- American Academy of Dermatology Association. “Seborrheic keratoses: overview”. https://www.aad.org/public/diseases/a-z/seborrheic-keratoses-overview
- National Health Service (NHS). “Seborrhoeic keratosis”. https://www.nhs.uk/conditions/seborrhoeic-keratosis/
- DermNet NZ. “Seborrhoeic keratosis”. https://dermnetnz.org/topics/seborrhoeic-keratosis
- Wollina U. “Seborrheic keratoses – the most common benign skin tumor of humans”. Open Access Macedonian Journal of Medical Sciences. 2018;6(11):2270-2275.
