Seborrhoeic or seborrheic keratoses are very common harmless skin lesions that appear during adult life. Seborrhoeic keratoses may also be called basal cell papillomas, senile warts or brown warts.
Seborrhoeic keratoses are harmless and rarely or never become malignant.
What do they look like?
They begin as slightly raised, skin coloured or light brown spots. Gradually they thicken and take on a rough, warty surface. They slowly darken and may turn black. These colour changes are harmless but may result in the lesion looking like a melanoma (a type of skin cancer).
They appear to stick on to the skin like barnacles.
Seborrhoeic keratoses appear on both covered and uncovered parts of the body. There may be one or many of them.
What causes seborrhoeic keratoses?
The cause of seborrhoeic keratoses is not known. The name is misleading, because they are not limited to a seborrhoeic distribution (scalp, mid-face, chest, upper back) as in seborrhoeic dermatitis, nor are they formed from sebaceous glands as is the case with sebaceous hyperplasia.
Seborrhoeic keratoses are considered degenerative in nature, appearing as part of the skin aging process. As time goes by, seborrhoeic keratoses become more numerous. Some people inherit a tendency to develop a very large number of them.
Skin cancers are sometimes difficult to tell apart from seborrhoeic keratoses, so if you are concerned or unsure about any skin lesion consult your doctor.
Very rarely, eruptive seborrhoeic keratoses may denote an underlying internal malignancy. The syndrome is known as the sign of Leser-Trelat.
Other types of seborrhoeic keratosis
Variants of seborrhoeic keratoses include:
- Some solar lentigines: flat brown marks in sun exposed areas
- Stucco keratoses: numerous small dry grey stuck-on lesions usually found on lower legs and feet
- Dermatosis papulosa nigra: numerous brown warty papules on face, neck and chest of dark-skinned individuals
- Irritated seborrhoeic keratosis: inflamed lesion, often red and crusted; may resemble a skin cancer
- Lichenoid keratosis: resolving keratosis or lentigo, often pink or grey-coloured
Dermatosis papulosa nigra
Irritated seborrhoeic keratosis
Seborrhoeic keratoses can easily be removed. The usual reason for removing a seborrhoeic keratosis is your wish to get rid of it. For example it may be unsightly, itch or rub against your clothes. Occasionally your doctor may recommend its removal because of uncertainty of the correct diagnosis.
Methods used to remove seborrhoeic keratoses include:
- Cryotherapy (liquid nitrogen) for thinner lesions
- Curettage & cautery
- Laser surgery
- Shave biopsy (shaving off with a scalpel)
On DermNet NZ:
- Ageing skin
- Brown marks and freckles
- Benign keratinocytic and adnexal tumours – common skin lesions course
- Stucco Keratosis – Medscape Reference
- Seborrheic Keratosis – Medscape Reference
- Seborrhoeic Warts – British Association of Dermatologists
- Patient information: Seborrheic keratosis (The Basics) – UpToDate (for subscribers)
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