Seborrhoeic keratoses are defined as a benign proliferation of epidermal keratinocytes. They present as raised, yellow-brown or black lesions and are often greasy and present in multiple sites. They usually appear on the trunk and vary between 1mm and several centimetres in size. They are often of little concern to the patient, although itching is sometimes a feature.
The most common appearance is a flat, verrucous plaque which appears "stuck on".
The aetiology is largely unknown. In some rare cases, occurrence can be linked with a familial trait which has an autosomal dominant mode of inheritance. Multiple eruption of seborrhoeic keratoses are sometimes linked to an inflammatory dermatosis, severe sunburn or as a manifestation of a visceral malignancy. The latter is usually cancer of the GI tract and is known as the sign of Leser-Trelat. The vast majority of cases, however, are idiopathic and require no further investigation.