by Nicole Evans M.D.

Created on: January 17, 2010   Last Updated: January 19, 2010

A seborrheic keratosis is a common, benign skin tumor.  These skin tumors develop from a proliferation of the epidermal level of the skin.  Seborrheic keratoses impart no risk for malignant transformation to skin cancer. 

Both men and women can develop seborrheic keratoses.  There is no significant difference in the frequency of appearance of seborrheic keratoses between men and women or among the various ethnicities.  These skin lesions do, however, occur more frequently in sun exposed areas, such as the arms and

face.  Seborrheic keratoses are very common in elderly individuals, as the incidence of seborrheic keratoses seems to increase with age.

Seborrheic keratoses can have a varying degree of pigmentation, ranging from yellowish to brown to black  The size of seborrheic keratotic lesions initially begins as less than a centimeter but the lesions can grow to several centimeters in diameter.  These benign skin tumors also often have less hair than the surrounding skin area. 

Seborrheic keratoses usually begin as flat, light-brown macules with sharply defined borders.  They then progress to a velvety or finely verrucous (fronded) surface.  With continued growth the seborrheic keratoses develop an uneven, warty surface with a dull appearance.  When a seborrheic keratosis is touched, it is often described as feeling oily or velvety. 

A clinical variant of a seborrheic keratosis are small polypoid (polyp-like) lesions.  Polypoid keratoses are often found around the neck or in the axillae (arm pit area).  These are commonly called skin tags but generally have a rougher surface than the more prevalent smooth skin tags. 

Seborrheic keratotic epidermal tumors are benign, as previously mentioned, but can be unsightly or catch on clothing and become irritated.  Many people will pick at seborrheic keratoses as the warty layer can often be flaked off.  However, picking or scratching will not make the lesion go away.  Rather, picking or scratching a seborrheic keratosis can cause the lesion to bleed and become inflamed or infected. 

Occasionally, an individual may develop numerous seborrheic keratoses.  In these cases, additional concerns do arise.  Most commonly, the patient may not notice a malignant melanoma that develops among the lesions.  This can put the patient at significant risk, as malignant melanoma is a lethal form of cancer.  Less commonly, an eruption of seborrheic keratoses can be a sign of a particular form of cancer called adenocarcinoma, especially adenocarcinoma of the gastrointestinal tract.

References:

Sperry K, Wall J: Adenocarcinoma of the stomach with eruptive seborrheic keratoses:   the sign of Leserp-Trélat. Cancer 1980 May 1; 45(9): 2434-7

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

Learn more about this author, Nicole Evans M.D..
Click here to send this author comments or questions.