These result from a localized hypertrophy of the basal cell layer of the epidermis. They are not caused by virus, but are included here for convenience. They are flat, brown or black excrescences 1/ 2 to 2 cms. in diameter, raised only slightly above the general surface, which are common on the trunk of patients aged forty-five or over though they may occur earlier. They may also appear on the temples or scalp. The surface is horny, and if pulled off leaves hypertrophied papillae projecting. They have to be distinguished from pigmented moles. Seborrhoeic warts are usually of shorter duration, and are present in greater numbers than pigmented moles; they give the appearance of being on rather than in the skin, and the way the surface can sometimes be pulled off is also a help in diagnosis. On the temples they must be distinguished from solar keratoses which may become malignant. Seborrhoeic warts never do this, Usually they cause no symptoms but occasionally they give rise to serve itching.
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