|Classification and external resources|
Many seborrheic keratoses on the back of a person with Leser–Trélat sign due to colon cancer.
A seborrheic keratosis (also known as "seborrheic verruca," and "senile wart":767:637) is a noncancerous benign skin growth that originates in keratinocytes. Like liver spots, seborrheic keratoses are seen more often as people age. In fact, they are sometimes humorously referred to as the "barnacles of old age".
The lesions appear in various colors, from light tan to black. They are round or oval, feel flat or slightly elevated (like the scab from a healing wound), and range in size from very small to more than 2.5 centimetres (1.0 in) across. They can resemble warts, though they have no viral origins. They can also resemble melanoma skin cancer, though they are unrelated to melanoma. Because only the top layers of the epidermis are involved, seborrheic keratoses are often described as having a "pasted on" appearance. Some dermatologists refer to seborrheic keratoses as "seborrheic warts"; these lesions, however, are usually not associated with HPV, and therefore such nomenclature is discouraged.
Presence and frequency increase with age: almost all elderly patients have some. An Australian study found 100% of the over-50-year-olds in their sample had at least one seborrhoeic keratosis (median number of 23 keratoses in the 51-75 year range, and 69 keratoses in the over-75-year-olds).
Onset is usually in middle age, although they are a common finding in younger patients—found in 12% of 15-year-olds to 25-year-olds—making the term "senile keratosis" redundant.
No difference in prevalence exists between genders. There is less prevalence in people with darker skin.
Seborrheic keratoses may be divided into the following types::769-770
- Common seborrheic keratosis (Basal cell papilloma, Solid seborrheic keratosis)
- Reticulated seborrheic keratosis (Adenoid seborrheic keratosis)
- Stucco keratosis (Digitate seborrheic keratosis, Hyperkeratotic seborrheic keratosis, Serrated seborrheic keratosis, Verrucous seborrheic keratosis)
- Clonal seborrheic keratosis
- Irritated seborrheic keratosis (Basosquamous cell acanthoma, Inflamed seborrheic keratosis)
- Seborrheic keratosis with squamous atypia
- Melanoacanthoma (Pigmented seborrheic keratosis)
- Dermatosis papulosa nigra
- Inverted follicular keratosis
Dermatosis papulosis nigra 
Commonly found among adult African Americans, presents on the face as small benign papules from a pinpoint to a few millimeters in size.
Stucco keratosis 
Visual diagnosis is made by the "stuck on" appearance, horny pearls or cysts embedded in the structure. Darkly pigmented lesions can be hard to distinguish from nodular melanomas. If in doubt, a skin biopsy should be performed. Thin seborrheic keratoses on facial skin can be very difficult to differentiate from lentigo maligna even with dermatoscopy.
Clinically, epidermal nevi are similar to seborrheic keratoses in appearance. Epidermal nevi are usually present at or near birth. Condylomas and warts can clinically resemble seborrheic keratoses, and dermatoscopy can be helpful. On the penis and genital skin, differentiation between condylomas and seborrheic keratoses can be difficult, even on biopsy.
When correctly diagnosed, no treatment is necessary. There is a small risk of localized infection caused by picking at the lesion. If a growth becomes excessively itchy or is irritated by clothing or jewelry, it can be removed.
Small lesions can be treated with light electrocautery. Larger lesions can be treated with electrodesiccation and curettage, shave excision, or cryosurgery. When correctly performed, removal of seborrheic keratoses will not cause much visible scarring except in persons with dark skin tones.
The causes of seborrheic keratosis are unclear. Because seborrheic keratoses are common on sun exposed areas such as the back, arms, face, and neck, ultraviolet light may play a role, as may genetics. However, they are also found on skin that has not been exposed to the sun.  A mutation of a gene coding for a growth factor receptor, (FGFR3), has been associated with seborrheic keratosis.
Although no direct cause-effect relationship between physiological stress and tumors in general has been medically established, medically, stress is recognized as a potential factor in the exacerbation of preexisting tumors, including those which are benign. Therefore, physiological stress has the potential to worsen a preexisting condition such as seborrheic keratosis.
- Freedberg, et. al. (2003). Fitzpatrick's Dermatology in General Medicine. (6th ed.). McGraw-Hill. ISBN 0-07-138076-0.
- James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0.
- Moles, Freckles, Skin Tags, Benign Lentigines, and Seborrheic Keratoses from the Cleveland Clinic website
- "Keratosis, seborrheic definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms". Medterms.com. 2012-03-19. Retrieved 2013-02-08.
- Seborrheic keratosis: Symptoms, from the Mayo Clinic website
- Yeatman JM, Kilkenny M, Marks R; The prevalence of seborrhoeic keratoses in an Australian population: does exposure to sunlight play a part in their frequency? Br J Dermatol. 1997 Sep;137(3):411-4. [abstract]
- Gill D, Dorevitch A, Marks R; The prevalence of seborrheic keratoses in people aged 15 to 30 years: is the term senile keratosis redundant? Arch Dermatol. 2000 Jun;136(6):759-62. [abstract]
- Busam Klaus J., Dermatopathology s.341; 2010 Saunders ISBN 978-0-443-06654-2
- Mehran Nowfar-Rad, MD. "Dermatosis Papulosa Nigra". Emedicine.medscape.com. Retrieved 2013-02-08.
- Raymond T. Kuwahara, MD. "Stucco Keratosis". Emedicine.medscape.com. Retrieved 2013-02-08.
- http://www.dermadoctor.com/article_Seborrheic-Keratoses_91.html[dead link]
- Seborrheic keratosis: Causes, from the Mayo Clinic website
- Hafner C, Hartmann A, Vogt T (2007). "FGFR3 mutations in epidermal nevi and seborrheic keratoses: lessons from urothelium and skin". J. Invest. Dermatol. 127 (7): 1572–3. doi:10.1038/sj.jid.5700772. PMID 17568799.
- Seborrheic, from Merriam-Webster's online medical dictionary
- Suffix "-osis" from the Merriam-Webster website
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