Disease Information

What is Seborrheic Keratosis?

A seborrheic keratosis (seb-o-REE-ik ker-uh-TOE-sis) is a common benign skin growth, similar to a mole. Most people will have at least one in their lifetime. They tend to appear in mid-adulthood and their frequency increases with age. They are harmless and don’t require treatment, but you can have them removed if they bother you.

Skin growths like seborrheic keratoses are sometimes also called epidermal tumors. That doesn’t mean they’re cancer, though. Technically, moles and warts are also epidermal tumors. That just means they are clusters of extra cells on the epiderma, the outer layer of the skin. They aren’t considered a risk factor for skin cancer.

What does Seborrheic Keratosis look like?

Seborrheic keratoses are roundish or oval-shaped patches on the skin with a “stuck on” appearance. They are sometimes described as waxy or scaly. They are raised above the skin and even when they are flat you can feel them with your finger. They are usually brown, but can also be black or tan, and less often, pink, yellow or white. They often appear in numbers.

Seborrheic keratoses are characterized by keratin on the surface — the same fibrous protein that fingernails, hooves, and horns are made of. This causes the textural details that often distinguish the growths. Sometimes it looks like small bubbles or cysts within the growth. Sometimes it looks scabby or wart-like. Sometimes it looks like the ridges and fissures in a brain.

Symptoms of Seborrheic Keratosis

What are the signs of seborrheic keratoses?
Seborrheic keratoses tend to:

• Start as small, rough bumps, then slowly thicken and develop a warty surface
• Have a waxy, stuck-on-the-skin look
• Be brown, though they range in color from white to black
• Range in size from a fraction of an inch to larger than a half-dollar
• Form on the chest, back, stomach, scalp, face, neck, or other parts of the body (but not on the palms and soles)
• Cause no pain, though some itch

Causes of Seborrheic Keratosis

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, nor are they associated with sebum — which is greasy.

Seborrhoeic keratoses are considered degenerative in nature. As time goes by, seborrhoeic keratoses become more numerous. Some people inherit a tendency to develop a very large number of them. Researchers have noted:

• Eruptive seborrhoeic keratoses can follow sunburn or dermatitis.
• Skin friction may be the reason they appear in body folds.
• Viral cause (eg human papillomavirus) seems unlikely.
• Stable and clonal mutations or activation of FRFR3, PIK3CA, RAS, AKT1 and EGFR genes are found in seborrhoeic keratoses.
• Seborrhoeic keratosis can arise from solar lentigo.
• FRFR3 mutations also arise in solar lentigines. These mutations are associated with increased age and location on the head and neck, suggesting a role of ultraviolet radiation in these lesions.
• Seborrhoeic keratoses do not harbour tumour suppressor gene mutations.
• Epidermal growth factor receptor inhibitors (used to treat cancer) often result in an increase in verrucal (warty) keratoses.

Who gets Seborrheic Keratosis?

Anyone can get one, but most commonly:

People who are 50 and older. They usually begin to appear in middle age, and rarely in younger people. About 30% of people have at least one by the age of 40, and about 75% by the age of 70.
People with a family history of it. About half of all cases of multiple seborrheic keratoses occur in families, suggesting that the tendency to develop many of them may be inherited.
Lighter-skinned people. Classic seborrheic keratosis as described here appears less frequently in darker-skinned people. However, a variant of seborrheic keratosis called dermatosis papulosa nigra is very common in darker-skinned people, including those of African, Asian and Hispanic descent.

How is Seborrheic Keratosis Diagnosed?

Examination. Dermatologists can usually identify a seborrheic keratosis with the naked eye.
Dermoscopy. If in doubt, your healthcare provider may look at the growth under a dermascope, a small, handheld lighted microscope.
Biopsy.** **If your healthcare provider suspects any cancer, they will want to take a sample — or remove the whole growth — to examine in a lab.

Complications of Seborrheic Keratosis

Seborrhoeic keratoses are not premalignant tumours. However:

• Skin cancers are sometimes difficult to tell apart from seborrhoeic keratoses.
• Skin cancer may by chance arise within or collide with a seborrhoeic keratosis.

Very rarely, eruptive seborrhoeic keratoses may denote an underlying internal malignancy, most often gastric adenocarcinoma. The paraneoplastic syndrome is known as the sign of Leser-Trélat. Eruptive seborrhoeic keratoses that are not associated with cancer are sometimes described as having pseudo-sign of Leser-Trélat.

Eruptive and irritated seborrhoeic keratoses may also arise as an adverse reaction to a medication, such as adalimumab, vemurafenib, dabrafenib, 5-fluorouracil and many chemotherapy drugs.

An irritated seborrhoeic keratosis is an inflamed, red and crusted lesion. It may give rise to eczematous dermatitis around the seborrhoeic keratosis. Dermatitis may also trigger new seborrhoeic keratoses to appear.

Reference:

https://my.clevelandclinic.org/health/diseases/21721-seborrheic-keratosis

https://dermnetnz.org/topics/seborrhoeic-keratosis

https://www.aad.org/public/diseases/a-z/seborrheic-keratoses-symptoms