Seborrheic keratosis is a common, harmless, noncancerous growth on the skin. It usually appears as a pale, black, or brown growth on the back, shoulders, chest, or face.
Seborrheic keratoses tend to appear from middle-age onwards. Some individuals may have just one, but normally there will be several. Seborrheic keratosis is not contagious.
Thirty percent of people have at least one by the age of 40 years, and they affect over 75 percent of people by the age of 70 years.
Seborrheic keratoses may look like warts, moles, or skin cancer. Their appearance is waxy, and they look as if they are stuck onto the skin. Some may look like a blob of brown candle wax.
Others resemble barnacles.
They can range in size from tiny to over 1 inch across.
They are not painful, but they may itch or become irritated. There are four dimensions to consider when describing seborrheic keratosis:
- Location: The growths are most commonly found on the scalp, shoulder, chest, abdomen, or back. They are never found on the soles of the feet or palms of the hands.
- Texture: Lesions usually start off as small, rough bumps, and they gradually get thicker and develop a warty surface. They can sometimes appear waxy and “stuck on.”
- Shape: They are usually round or oval.
- Color: Most are brown, but they can be yellow, black, or white.
The lesions are rarely painful, but they can be annoying, depending on their position. It is important not to pick or scratch them as this can lead to bleeding, swelling, and, potentially, infection.
When to visit a doctor
If the following occur, a doctor’s opinion should be sought:
- a large number of growths grow in a short space of time
- the borders around the growths are irregular or blurred
- the growths are irritated by clothes and regularly bleed, removal may be an option
- growths or sores develop and do not heal
- if the growths are an unusual color; for instance, purple, reddish-black, or blue
In most cases of seborrheic keratosis, no further treatment is necessary.
The doctor may recommend removing the growth if:
- it is hard to distinguish from skin cancer, or if the diagnosis is uncertain
- the patient does not like it, and wants it removed
- it causes problems, for example, itching or irritation with clothing or jewelry rubbing against it
If the dermatologist carries out a biopsy, they will normally remove the seborrheic keratosis at the same time.
There are several ways of removing seborrheic keratosis.
Liquid nitrogen is applied to the growth with a spray gun or cotton swab. The lesion freezes and falls off in a few days. A blister may form when the growth falls off; this will eventually dry into a crust, which will fall off.
Electrocautery, curettage, or both
In electrocautery, also known as electrosurgery, the surgeon uses an electric current to burn (cauterize) the growth, under a local anesthetic. In curettage, a curette – a scoop-shaped surgical instrument – is used to scrape off the burnt growth.
Some patients may require just electrocautery, some curettage, and others both.
Ablation involves vaporizing the growth with a laser.
All the methods of removal above have disadvantages. For example, the skin in the area of the seborrheic keratoses may be lighter, and therefore leave a lighter mark where the lesion once was. Also, there is no way to remove multiple lesions in a single intervention.
In most cases, the growth does not return, but new ones may appear in other areas of the body.
There are no proven home remedies for seborrheic keratosis. Lemon juice or vinegar may cause irritation, possibly causing the lesion to dry and crumble, but there is no evidence that this is safe or effective.
Some substances, such as tea tree oil, can trigger allergic contact dermatitis, an immune system reaction that causes itching and inflammation around the site.
Anyone who is concerned about a lesion should see a doctor, if only to check that it is not melanoma.
Dermatologists are not certain why seborrheic keratoses develop.
Possible causes and risk factors include:
- Sunlight: Lesions commonly appear on parts of the body that are more exposed to sunlight. Ultraviolet (UV) light may play a role. However, they can develop in areas rarely exposed to sunlight, so this is not the whole answer.
- Genetics: Seborrheic keratosis seems to run in families. Scientists have suggested that a genetic mutation could be responsible.
- Age: They are more likely to develop in those aged 50 years or above.
Seborrheic keratoses are not believed to be related to any viral infection. Skin friction may be a factor, as they often appear in skin folds.
To diagnose seborrheic keratosis, a physician will carry out a visual and physical examination.
The lesions can be solitary or in groups, for example on the scalp, under the breasts, over the spine, or in the groin area.
A lesion that has the features of seborrheic keratosis is highly unlikely to be skin cancer.
However, the darker lesions sometimes look like melanoma, a kind of skin cancer. In this case, the doctor may recommend taking a biopsy for examination under a microscope.
Researchers who analyzed biopsies from 9,204 people diagnosed with seborrheic keratosis, at Massachusetts General Hospital and Harvard Medical School in Boston, MA, found that only 61 cases, or 0.66 percent, were actually melanoma.
If the seborrheic keratosis is on the skin, and it is very thin, there is a small possibility that it could be a kind of skin cancer known as lentigo maligna.
If multiple seborrheic keratoses develop in a short period of time, it is advisable to seek medical attention, as this may be a sign of internal cancer.
However, seborrheic keratosis is unlikely to indicate cancer, and most dermatologists consider seborrheic keratosis little more than a nuisance.
Nevertheless, researchers from Atlanta, GA, have suggested that these lesions “should get our respect” because the gene process used by the lesions may be useful for studying certain types of cancer.
Since seborrheic keratoses are so common, share features with some cancers, but rarely become malignant, this could make them a useful subject of research into other, more serious diseases.