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Glossary


Risk factors for non-melanoma skin cancer

Any substance or condition that increases cancer risk is referred to as a risk factor. The most important risk factor for developing non-melanoma skin cancer is exposure to ultraviolet radiation (UVR). However, most cancers are the result of many risk factors.

 

Risk factors*

Possible risk factors

Sun and ultraviolet radiation (includes tanning beds and sunlamps)

Having a fair complexion

Personal history of skin cancer

Exposure to ionizing radiation

Exposure to arsenic

Exposure to specific chemicals

PUVA therapy

Xeroderma pigmentosum

Basal cell nevus syndrome

Weakened immune system

Precancerous skin conditions

Human papillomavirus (HPV)

Photosensitizing agents

Number of moles

*Risk factors are generally listed in order from most significant to least significant. In most cases, it is impossible to rank the relative significance of individual risk factors with absolute certainty.

 

Non-melanoma skin cancer affects more men than women. This may be because men tend to spend more time outside exposed to the sun. The risk of basal and squamous cell skin cancers increases as people get older. Most skin cancers appear after the age of 50, but can be seen in younger people.

 

The following factors are known to increase the risk of developing non-melanoma skin cancer.

Sun and ultraviolet radiation

Ultraviolet radiation (UVR) is the most important risk factor for developing skin cancer. The 3 types of UVR are UVA, UVB and UVC. The main source of UVR is the sun. Most skin cancers are caused by long-term exposure to the sun.

 

Squamous cell carcinoma has been linked to long-term exposure to UVR. People who work outside, such as farmers, have a higher risk of developing skin cancer because they are exposed to UVR from the sun for long periods of time. People who live at high altitudes or in areas with year-round, bright sunlight also have a greater risk of developing skin cancer. Squamous cell carcinoma has been most strongly linked to total lifetime sun exposure, recreational and occupational exposure and childhood overexposure to UVR.

 

Basal cell carcinoma is most common in fair-skinned people. It has been most strongly linked to intermittent exposure to UVR, sunburns and overexposure during the childhood or teenage years.

 

Indoor tanning equipment, such as tanning beds and sun lamps, is also a source of UVR. A tan is evidence of skin damage from exposure to UVR. Just like the sun, indoor tanning equipment gives off UVR  that can cause melanoma, squamous cell carcinoma, sunburns, premature aging and cataracts.

 

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Having a fair complexion

Having a fair complexion increases a person's risk of non-melanoma skin cancer. People with fair skin or a light complexion are at a higher risk of developing this disease than people with other skin types. This includes:

  • skin that burns easily, freckles and doesn’t tan
  • blue, green or other light-coloured eyes
  • red or blond hair

 

The risk of skin cancer is greater for this group of people because the skin has less pigment (melanin) to act as a protective factor against UVR. People most at risk are those who had intense exposures to the sun at an early age that resulted in sunburns.

 

Albinism is an inherited genetic condition that causes a lack of pigment (melanin) in skin, eyes and hair. People with this condition burn easily, increasing their risk of developing non-melanoma skin cancer.

 

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Personal history of skin cancer

People who have had non-melanoma or melanoma skin cancer have a much greater risk of developing non-melanoma skin cancer and a somewhat higher risk of developing melanoma.

 

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Exposure to ionizing radiation

People who have had radiation therapy in the past have a greater risk of developing non-melanoma skin cancer in the treatment area. These second cancers can develop 15–20 years after they received radiation therapy.

 

Radiation exposure from nuclear fallout, such as in Hiroshima, Japan, is associated with an increased risk of developing non-melanoma skin cancer.

 

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Exposure to arsenic

Exposure to arsenic increases the risk of developing non-melanoma skin cancer. Arsenic and arsenic-containing compounds are found in certain types of wood preservatives, pesticides and insecticides. People who work in mining and smelting industries, and those who manufacture and apply pesticides and insecticides, can be exposed to arsenic. However, the biggest exposure to arsenic is through drinking waterthat contains high levels of arsenic.

 

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Exposure to specific chemicals

Occupational exposure to certain petroleum products, such as coal and shale, industrial tar and pitch, creosote, chimney soot and paraffin, increases the risk of developing non-melanoma skin cancer.

 

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PUVA therapy

PUVA (psoralen + UVA) therapy is a common treatment for skin conditions like psoriasis. The drug psoralen is given to make the skin more sensitive to UVA light. Long-term PUVA therapy increases a person's risk of developing squamous cell carcinoma.

 

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Xeroderma pigmentosum

Xeroderma pigmentosum (XP) is a rare genetic disease that affects the skin's ability to repair damage caused by the sun. It is characterized by greater sensitivity to UVR, skin colour changes, premature skin aging and skin cancer. People with XP have a high risk of developing both melanoma and non-melanoma skin cancer.

 

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Basal cell nevus syndrome

Basal cell nevus syndrome (also known as Gorlin syndrome or nevoid basal cell carcinoma syndrome) is a rare genetic disorder. It causes multiple defects involving the skin, eyes, nervous system, endocrine glands and jawbone. People with this syndrome have a high risk of developing multiple basal cell skin cancers. The cause of this disorder is a mutation in a gene that suppresses tumours, known as the patched 1 gene (PTCH1).

 

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Weakened immune system

People who have a weakened immune system or who must take drugs to suppress their immune system following an organ transplant have an increased risk of developing non-melanoma skin cancer.

 

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Precancerous skin conditions

People who have been diagnosed with precancerous skin conditions are at higher risk of developing non-melanoma skin cancer. These conditions include actinic keratosis (a non-cancerous growth), arsenic keratosis and Bowen’s disease.

 

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Possible risk factors

The following factors have some association with non-melanoma skin cancer, but there is not enough evidence to say they are known risk factors. Further study is needed to clarify the role of these factors for non-melanoma skin cancer.

  • human papillomavirus (HPV)
    • There are several different strains of human papillomavirus (HPV), some of which cause warts in the genital and anal area. Infection with HPV may cause skin cancer in this area of the body. HPV may also be a risk factor for squamous cell cancer of the lip.
    • A rare inherited genetic condition called epidermodysplasia verruciformis makes people more susceptible to chronic skin infections caused by HPV. These wart-like lesions are brown or reddish and scaly. They appear in patches on the trunk, hands, arms, legs and face. They can become cancerous after the age of 30.
  • photosensitizing agents – Photosensitizing agents make the skin unusually sensitive to ultraviolet light. People taking drugs that have photosensitizing agents can develop sunburn or rashes after a period of sun exposure that would not normally affect them. Some drugs that have photosensitizing agents include:
    • antihistamines
    • oral contraceptives and estrogen
    • nonsteroidal anti-inflammatory drugs (NSAIDs)
    • phenothiazines
    • psoralens (used in PUVA therapy for psoriasis)
    • sulphur drugs, such as sulphonamides and sulphonylureas
    • thiazide diuretics
    • tetracyclines
    • tricyclic antidepressants
    • chemotherapy drugs
    • anti-parasitic drugs
    • oral hypoglycemics
  • number of moles – Some studies have found that the greater the number of moles (nevi) that a person has, the greater their risk of developing basal cell carcinoma. This is especially true for women.

 

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Unknown risk factors

The following are factors for which there is not enough evidence or the evidence is inconclusive. In other words, it can't be determined for sure whether these risk factors are or are not associated with non-melanoma skin cancer.

  • skin trauma
  • smoking
  • eating unmodified dairy products (such as whole milk, cheese and yogurt)
  • selenium supplementation

 

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See a list of questions to ask your doctor about risks.

References

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