Causes and Risk Factors of Merkel Cell Carcinoma

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Merkel cell carcinoma often appears on areas of the body that receive the most sunlight like the face and neck. A Merkel cell carcinoma growth looks like a pearly, pimple-like lump on the skin. Known risk factors for Merkel cell carcinoma include exposure to ultraviolet (UV) rays, a compromised immune system, a history of skin cancer, and fair skin.

In this article, we will discuss the causes of Merkel cell carcinoma and how to reduce your risk. 

How to Lower Risk of Merkel Cell Carcinoma

Verywell / Shideh Ghandeharizadeh

Common Causes

Cancer is caused both by genetic changes in the DNA of our cells and epigenetic changes (caused by our behaviors and the environment) in gene control structures present inside the cell.

Merkel cell carcinoma does not run in families and does not appear to be genetic. However, there are known risk factors that greatly increase your chances of being diagnosed with Merkel cell carcinoma. 

Exposure to Ultraviolet Rays

The greatest risk for Merkel cell carcinoma is unprotected exposure to the sun or a tanning bed. UV rays from the sun or tanning beds can damage your skin and suppress the immune system's response. These cells then have a reduced ability to repair cell damage and fight cancerous cells. 

Suppressed Immune System

People with a compromised immune system are at higher risk of developing Merkel cell carcinoma. In fact, the risk may be as much as 15 times greater than for those with healthy immune systems. And more than 90% of Merkel cell carcinoma cases occur in people with suppressed immune systems. 

The immune system can be compromised by a disease like human immunodeficiency virus (HIV), other forms of cancer, or immunosuppressive medications used to treat autoimmune diseases such as rheumatoid arthritis (RA) and multiple sclerosis (MS). An autoimmune disease occurs when the immune system attacks healthy cells by mistake.

Merkel Cell Polyomavirus

Merkel cell polyomavirus is a common virus that is found on the skin. It usually causes no signs or symptoms. The virus is found in the cancer cells of about 80% of people with Merkel cell carcinoma. Because Merkel cell polyomavirus is very common and Merkel cell carcinoma is very rare, researchers are unsure how closely the two are linked.

Fair Skin

People with fair skin are at greater risk of developing skin cancer than those with darker complexions. More than 90% of people diagnosed with Merkel cell carcinoma are White, and this is likely due to the fact that darker skin is better protected against UV rays.


The risk of Merkel cell carcinoma increases with age. About 80% of people with this rare type of skin cancer are over age 70. Researchers believe that this may be because skin experiences more sun damage over time. Your immune system also tends to weaken with age.


Men are twice as likely to be diagnosed with Merkel cell carcinoma as women. Researchers believe this may be related to men receiving more sun exposure in general.


Risk factors for Merkel cell carcinoma include exposure to UV rays, a compromised immune system, Merkel cell polyomavirus, fair skin, older age, and male sex.

How to Lower Your Risk

While you may not be able to address all of the risk factors, such as having a compromised immune system, there are important steps that you can take to lower your risk of developing Merkel cell carcinoma. One such step is reducing exposure to UV rays.

To protect your skin from UV rays:

  • Wear sunscreen every day, including on cloudy or rainy days. Choose a waterproof, broad-spectrum sunscreen with a sun protection factor (SPF) of 30 or higher. 
  • Avoid being outside in the sun during the hours of 10 a.m. to 2 p.m. This is when the sun’s rays are the strongest. Stay indoors or in the shade. 
  • Cover your skin when you’re outside with a lightweight long-sleeve shirt, pants, sunglasses, and a hat. 
  • Avoid smoking and tanning beds.


Merkel cell carcinoma occurs when skin cells are damaged and start to grow at an out-of-control rate. Risk factors for this rare type of skin cancer include UV ray exposure, immunosuppression, and fair skin. To lower your risk for Merkel cell carcinoma, protect yourself from the sun with lightweight clothing, shade, and sunscreen. 

A Word From Verywell

If you have recently been diagnosed with Merkel cell carcinoma, it’s natural to want answers about why this happened. While physicians and scientists are always learning more about this rare type of cancer, we know that a leading risk factor is unprotected exposure to UV rays from the sun or tanning bed. To lower your risk, always protect your skin when out in the sun and avoid tanning beds. 

Frequently Asked Questions

  • What does Merkel cell carcinoma look like?

    Merkel cell carcinoma usually appears as a single, painless lump on the skin. It is often red or purple in color and looks shiny or pearl-like. 

  • How is Merkel cell carcinoma diagnosed?

    Merkel cell carcinoma is usually diagnosed with a physical exam, a detailed history, and a skin biopsy (removing a sample of tissue for further examination). Your doctor may also recommend imaging studies to determine if the cancerous cells have spread beyond the primary tumor (the first tumor that developed). 

  • Is Merkel cell carcinoma curable?

    Merkel cell carcinoma is an aggressive cancer but can be treated when caught early. This type of skin cancer has a high rate of recurrence because it spreads quickly. Studies show that about 30% of patients already have metastases (tumors that have spread) at the time of diagnosis. 

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Carrie Madormo, RN, MPH
Carrie Madormo, RN, MPH, is a health writer with over a decade of experience working as a registered nurse. She has practiced in a variety of settings including pediatrics, oncology, chronic pain, and public health.