Seborrhoeic keratosis, also known as "verruca seborrhoeica", is a benign lesion that is very common in older people of both sexes. The lesions are sharply demarcated, flat or raised papules or plaques. They are often flesh-coloured, slightly yellowish or hyperpigmented. They are usually small, entirely exophytic lesions a few mm in diameter, but they can reach larger sizes.

Seborrhoeic keratosis is a type of skin growth. It may look unattractive and embarrass the patient, but the growths are not harmful. In some cases, however, it can be difficult to distinguish seborrhoeic keratosis from melanoma, a very serious type of skin cancer. Although seborrhoeic keratoses are often confused with warts, they are quite different from them. Seborrhoeic keratosis is a non-cancerous growth of the upper part of the skin. It can occur singly or in groups. They are usually brown but can range from light brown to black. Their size can vary greatly. Their surface looks waxy. Sometimes they look as if brown wax had dripped onto the skin.

What causes seborrhoeic keratosis?
The real cause of seborrhoeic keratosis is not known. However, everyone may have a few of these growths. They become more common with age. Some people develop many seborrhoeic keratoses over time, while others develop fewer. Seborrhoeic keratoses can be seen in pregnancy, in people receiving oestrogen treatment or together with certain medical problems.

Where do they occur?
Although seborrhoeic keratoses can be seen on the scalp, face, neck and anywhere on the body, they are most often found on the chest and back. They are less common below the waist. Because the sun does not affect the appearance of seborrhoeic keratoses, they can also be seen in areas not exposed to the sun. When they first appear, they are small bumps with a rough surface. They later thicken and take on a wart-like surface.

There is usually more than one growth. The growths can be found on various parts of the body, including:

* Chest
* Shoulders
* Back
* Abdomen

The growths are not found on the soles of the feet or the palms of the hands.

Is seborrhoeic keratosis important?
Everyone may have a few of these growths. Although they may appear suddenly, seborrhoeic keratoses are not a sign of serious disease and are not related to skin cancer.

Especially on the face, they may not be raised above the skin. Rubbing by clothing can irritate seborrhoeic keratoses. Over the years seborrhoeic keratoses can grow, itch, become irritated and bleed. In this case they need to be treated. Seborrhoeic keratoses can turn black, in which case they can be difficult to distinguish from skin cancers. In this situation the seborrhoeic keratosis should be surgically removed and examined under the microscope to distinguish it from cancer.

Can seborrhoeic keratosis be prevented?
Ointments and medicines do not provide a complete cure and do not prevent seborrhoeic keratosis.

How are they treated?
Most seborrhoeic keratoses are treated with one of 3 methods. The first method is cryosurgery, or freezing. A very cold gas called liquid nitrogen is applied to the seborrhoeic keratosis. A blister forms under the seborrhoeic keratosis, which dries to form a crust. Within a few weeks the keratosis falls off. When it heals, no mark remains. Occasionally a small white or dark spot may remain.

Another method is known as curettage. These growths are scraped off with a curette. After the area has been numbed with an injection or spray, the seborrhoeic keratosis is removed from the skin. No stitches are needed and bleeding is minimal; it can easily be stopped by applying pressure. Electrosurgery is another treatment method. The skin is first numbed, and then an electric current is applied and the lesion is scraped away.