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Seborrhoeic Keratosis (Waxy lesion)

What are seborrhoeic keratoses?

Seborrhoeic keratoses are harmless brown growths that are one of the most common skin blemishes. They give the appearance of sitting loosely on the skin. Some people refer to them as delayed birthmarks, while others unkindly call them barnacles of old age. The cause is unknown. They are more common with advancing age and in those with a family history of these lumps.

Where are they located?

Although they can occur anywhere, they are usually found on the face and trunk (chest and back).

What are the features of seborrhoeic keratoses?

The raised lumps have the following characteristics:

• A flat top with a well-defined border.

• A pitted surface.

• Sometimes a waxy or greasy crusty surface.

• The appearance of sitting on the skin.

• Usually round or oval, but can be any shape.
• Colour varies from yellow to dark brown, occasionally black.

• Size varies from a few millimetres up to five centimetres (two inches) or larger.

Seborrhoeic keratoses may look as if a dried sultana has been pressed onto the skin. Others may have a surface resembling a currant bun. They may be solitary or, more commonly, multiple. The lumps are asymptomatic, causing no itch or pain.

Who gets them?

Any adult may be affected and they are equally common in both sexes. Seborrhoeic keratoses are age related, increasing in number and degree of darkness with advancing age. They are rare in people younger than 40 and usually start to appear after the age of 50, when they are flat, lightcoloured and inconspicuous. By age 60, almost everyone has a few seborrhoeic keratoses.

What happens to them?

Usually, they gradually get larger, darker and increase in number. Sometimes they are rejected by the body and fall off, leaving a pale area on the skin. However, most remain permanently.

Do they pose any risk?

There is no risk. They are not contagious or infectious and do not become malignant (cancerous). If they are very dark they may cause concern because they resemble a melanoma, but your doctor can reassure you about this problem. Many people are inclined to scrape them with their fingernails. This habit is not recommended because they can become infected. They also invariably grow back.

What is the treatment?

There are no tablets or ointments to cure or prevent these growths. Their removal is not recommended because they are harmless and can be safely left untreated. However, ugly seborrhoeic keratoses affecting a person’s appearance and those that keep catching on clothing can be removed by various methods, including surgical excision. Others, especially thin ones, can be shrunk or decoloured by carefully applying liquid nitrogen or other strong chemicals to the surface.