Causes and Risk Factors of Skin Cancer

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We don't know exactly what causes skin cancer, but risk factors may include skin tone and ethnicity, sun exposure and sunburns, exposure to environmental chemicals and other substances, some medical conditions or treatments for medical problems, and smoking. A family history of skin cancer, as well as some genetic syndromes, can raise the risk, and genetic factors are thought to play an important role in the development of many non-melanoma and melanoma skin cancers. On a more positive note, nutritional factors, such as a diet rich in fruits and vegetables, may reduce the risk.

skin cancer causes and risk factors
Illustration by Verywell 

Risk Factors

Risk factors may include exposures that directly damage the skin, causing the changes in DNA (gene mutations) that can lead to cancer developing. Other factors, such as immune suppression, can reduce the ability of the body to repair cells after damage occurs. 

The importance of specific risk factors can vary based on skin type and more. Common risk factors for skin cancer include:

Age

In general, non-melanoma skin cancers (like basal cell carcinomas and squamous cell carcinomas) increase with age, though melanomas are often found in young people.

melanoma: newly diagnosed cases
Illustration by Verywell 

Skin Tone, Ethnicity, and Body Features

Skin tone can be a significant risk factor for the development of skin cancer. People who have fair skin having the highest risk because the pigment melanin (responsible for skin color) offers some protection from ultraviolet (UV) radiation and they simply have less of it than those with dark skin.

That said, people with any skin color may develop skin cancer, and though the disease is more common in whites than in blacks, blacks are more likely to die from the disease. This increased risk of death is related to both the increased difficulty in detecting the condition in people with darker skin (so that it is found in later stages of the disease) and decreased access to medical care. And, just as melanoma is increasing in whites, it is increasing in Latinos as well.

People with any of the following characteristics have the greatest risk of skin cancer:

  • Freckles
  • Fair skin tone
  • Skin that does not tan or that tans poorly
  • Skin that burns easily
  • Light colored eyes, such as green or blue
  • Naturally red or blonde hair (the former carries more risk than the latter)

UV Exposure

Sun exposure accounts for 70 percent of skin cancers, posing the greatest risk factor. Squamous cell carcinoma, however, is the type most closely tied to sun exposure. The amount of ultraviolet (UV) light exposure depends on the strength of the light (which can vary with the angle of the sun), the length of exposure, and whether the skin was covered with clothing or sunscreen.

A severe sunburn at a young age, even if it only occurred once, can be a significant risk factor even decades later. Sunburns are associated most strongly with melanoma, and sunburns to the trunk of the body are associated with the greatest risk.

While sun exposure plays a role in all the major types of skin cancer, the type of cancer varies with the pattern of exposure. Squamous cell carcinoma and basal cell carcinoma are linked most closely with long-term exposure, and those who spend more time outdoors for work or play have a higher risk. In contrast, melanoma is associated with infrequent but intense sun exposure (think spring break in a warm place).

In other words, everyday, routine sun exposure (even on a cloudy day) is a risk factor just like spending some time at the beach or a tanning salon, although regular exposure is correlated more closely with squamous cell cancers and sunbathing with melanoma.

Environmental Chemicals

Exposure to chemicals and other substances at home or on the job can increase the risk of skin cancer. Substances linked to an increased risk include:

  • Arsenic: From chronic ingestion in drinking water (especially private wells) as well as occupational exposure.
  • Tar (such as with highway workers)
  • Paraffins (wax): Paraffins are commonly used in automobile manufacturing.
  • Solvents, especially aromatic and chlorinated solvents (common for metal workers and those exposed to printing inks, degreasers, and cleaning products)
  • Vinyl chloride (such as in factories that produce vinyl products)

Smoking

Smoking is associated with an increased risk of squamous cell carcinomas of the skin, but not basal cell carcinomas. A 2017 study found that the risk of basal cell cancers was actually significantly lower in smokers, but this may be due to detection bias (the researchers may have found cancers that would otherwise have gone undetected in a person, not in the study). Unlike cancers such as lung cancer, the risk of skin cancer in former smokers drops to that of never smokers after quitting.

Conditions and Treatments

There are a number of skin conditions that can either increase the risk of developing skin cancer or are considered precancerous. In addition, some treatment modalities for them may raise the risk of cancer. Some of these conditions include:

  • Previous skin cancer: Those who have had a non-melanoma skin cancer are around 10 times more likely than average to develop another of these cancers. Those who have had a melanoma are three times more likely to develop a non-melanoma skin cancer.
  • Actinic keratosis: Actinic keratoses (solar keratoses) are very common skin lesions that appear as rough, scaly, wart-like patches on the skin and can be pink, red, or brown. They are most common in sun-exposed areas of the body. Actinic keratoses are considered to be precancerous and, in fact, some dermatologists believe that it may be an early form of squamous cell carcinoma of the skin. It's thought that 20 percent to 40 percent of this type of skin cancer begin this way, and a 2018 review noted that exactly where actinic keratoses forms may indicate the likelihood it will progress to skin cancer. Areas of most concern include the backs of the hands, the forearms, the legs, and around the eyes, lips, or nose. People who have many actinic keratoses are also more likely to develop basal cell carcinoma or melanoma.
  • Having many moles (more than 50)
  • Dysplastic moles (abnormal appearing moles)
  • Congenital melanocytic nevi: These are large moles present at birth, and melanoma may develop in up to 10 percent of these lesions (especially very large nevi).
  • Skin that has endured a severe burn or is inflamed

Psoralens or ultraviolet (UV) therapy for psoriasis or eczema may also increase the risk of developing a non-melanoma skin cancer.

Likewise, non-skin conditions and treatments may also affect your risk. These can include:

  • Immune system deficiencies, either hereditary or acquired (such as with HIV/AIDS)
  • Human papillomavirus (HPV) infections: Some strains of HPV may contribute to cancers in the tissues of the genitalia, anus, and skin around the fingernails.
  • Certain medications that increase sun sensitivity (photosensitivity), including a few antibiotics, the high blood pressure drug hydrochlorothiazide, and some chemotherapy medications
  • Previous radiation therapy for cancer: The increased risk is present only in the areas where radiation was received.

Diet

While specific foods that raise the risk of skin cancer have not been identified, there is evidence that some dietary habits are associated with a lower risk of the disease. A diet high in fruits and vegetables may reduce the risk of developing skin cancer, due to the antioxidants present in the phytochemicals (plant-based chemicals) found in these foods.

Genetics

The influence that genetics plays in the development of skin cancer can vary depending on the particular type. It can be difficult to separate out risk related to genetics and hereditary characteristics, such as skin tones.

Identical twin studies suggest that almost half of a person's risk for basal cell and squamous cell carcinomas is caused by genetic factors. While known inherited gene mutations account for only around 1 percent of melanomas, a 2016 study suggested that up to 58 percent of melanoma risk is related to inherited factors.

It's not certain how much having a family history of skin cancer affects risk, though it's clear there is a link. In Sweden, a country that maintains a large family-cancer database, a large study found that the risk of squamous cell carcinoma was two to four times the average if a first-degree relative (parent, sibling, or child) had skin cancer. A family history of atypical nevus syndrome increases the risk of melanoma.

There are several hereditary syndromes that raise the risk of a person developing skin cancer. A few of the more common ones include:

  • Basal cell carcinomas: People with basal cell nevus syndrome have a greater risk of developing basal cell carcinomas (PTCH1 and PTCH2 gene mutations).
  • Squamous cell carcinomas (SCC): The risk of SCC is increased in those with xeroderma pigmentosum, oculocutaneous albinism, epidermolysis bullosa, and Fanconi anemia.
  • Melanoma: An abnormality in tumor suppressor gene CDKN2A is responsible for up to 40 percent of familial melanomas A number of other gene mutations are also associated with melanoma, including BRCA2 gene mutations.
Diagnosing Skin Cancer
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