SUPPORT CANADIANS LIVING WITH CANCER
Risk factors for non-melanoma skin cancer
A risk factor is something that increases the risk of developing cancer. It could be a behaviour, substance or condition. Most cancers are the result of many risk factors. Exposure to ultraviolet radiation (UVR) from the sun, tanning beds or sun lamps is the most important risk factor for non-melanoma skin cancer.
The risk of basal cell and squamous cell skin cancers increases as you get older. Most skin cancers appear after the age of 50, but they can also be seen in younger people. If basal cell carcinoma (BCC) develops in people under the age of 52, it is more common in women than men. In people older than 52, BCC is more common in men. Squamous cell carcinoma (SCC) occurs equally in both men and women up to the age of 47. After the age of 47, SCC becomes more common in men.
Risk factors are generally listed in order from most to least important. In most cases, it is impossible to rank them with absolute certainty.
Known risk factors
There is convincing evidence that the following factors increase your risk for non-melanoma skin cancer.
Exposure to ultraviolet radiation (UVR) is the most important risk factor for developing skin cancer. The 3 types of UVR are UVA, UVB and UVC.
The sun is the main source of UVR. 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, non-melanoma skin cancer, sunburns, premature aging and cataracts.
Most skin cancers are caused by exposure to the sun over a long period of time. People who work outside, such as farmers, have a higher risk of developing skin cancer because they are exposed to UVR. 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 (SCC) has been most strongly linked to total lifetime sun exposure. This includes recreational and occupational exposure, and being exposed to UVR a lot during childhood.
Basal cell carcinoma (BCC) is most common in people with fair complexion. It has been most strongly linked to on-and-off exposure to UVR, sunburns and overexposure during the childhood or teenage years.
People with fair or light-coloured skin have a higher risk of developing non-melanoma skin cancer than people with other skin types. People with blonde or red hair and blue, green or grey eyes also have a higher risk of developing non-melanoma skin cancer. Their risk is greater because people with these features have less melanin. Melanin is what gives colour to your skin, hair and eyes. Experts think that it also helps protect the skin from UVR.
People with a fair or light-coloured skin who had very bad sunburns at an early age have the highest risk for non-melanoma skin cancers.
Albinism is an inherited genetic condition that causes a lack of melanin in the skin, eyes and hair. People with this condition burn easily, increasing their risk of developing non-melanoma skin cancer.
People who have already had non-melanoma or melanoma skin cancer have a much greater risk of developing non-melanoma skin cancer. They also have a somewhat higher risk of developing melanoma.
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 linked with a higher risk of developing non-melanoma skin cancer.
Exposure to arsenic increases the risk of developing non-melanoma skin cancer. Arsenic is a naturally occurring substance found in rocks and soil. Arsenic and compounds that contain arsenic are also found in certain types of wood preservatives, pesticides and insecticides.
People who work in mining and smelting industries can be exposed to arsenic. People who manufacture and apply pesticides and insecticides may also be exposed to arsenic.
The biggest risk of exposure to arsenic is through drinking water that contains high levels of arsenic. Arsenic can get into drinking water from natural sources or from certain types of mining, smelting or manufacturing plants.
Occupational exposure to certain petroleum products increases the risk of developing non-melanoma skin cancer. These products include coal and shale, industrial tar and pitch, creosote, chimney soot and paraffin.
PUVA is a common treatment for skin conditions like psoriasis. It uses the drug psoralen and UVA radiation. Psoralen makes the skin more sensitive to UVA light. Receiving PUVA therapy for a long period of time increases your risk of developing squamous cell carcinoma (SCC).
Xeroderma pigmentosum (XP) is a rare inherited condition that affects the skin so it can’t repair sun damage. When someone has XP, their skin is more sensitive to UVR so that it changes colour and ages prematurely. People with XP also have a high risk of developing both melanoma and non-melanoma skin cancer.
Basal cell nevus syndrome is also known as Gorlin syndrome or nevoid basal cell carcinoma syndrome. It is a rare inherited condition caused by a mutation in a gene that suppresses tumours, known as the patched 1 gene (PTCH1).
Basal cell nevus syndrome causes different problems with the skin, eyes, nervous system, endocrine glands and jawbone. People with this syndrome also have a high risk of developing many basal cell carcinomas.
People with a weakened immune system have a higher risk of developing non-melanoma skin cancer. The immune system can be weakened by certain diseases. It can also be weakened by drugs that people need to take to suppress their immune system following an organ transplant.
People who have been diagnosed with precancerous skin conditions have a higher risk of developing non-melanoma skin cancer. These conditions include actinic keratosis and Bowen’s disease.
The following factors have been linked with non-melanoma skin cancer, but there is not enough evidence to show 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 (SCC) of the lip.
A rare inherited genetic condition called epidermodysplasia verruciformis makes people more vulnerable to chronic skin infections caused by HPV. These infections look like warts and 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 make the skin unusually sensitive to ultraviolet light, which may increase the risk for non-melanoma skin cancer. People taking drugs that have photosensitizing agents can develop sunburn or rashes after being in the sun for even short periods of time. Some drugs that have photosensitizing agents include:
- oral contraceptives and estrogen
- nonsteroidal anti-inflammatory drugs (NSAIDs)
- psoralens (used in PUVA therapy for psoriasis)
- sulphur drugs, such as sulphonamides and sulphonylureas
- thiazide diuretics
- tricyclic antidepressants
- chemotherapy drugs
- antiparasitic drugs
- oral hypoglycemics
Number of moles
Some studies have found that the greater the number of moles, or nevi, that a person has, the greater their risk of developing basal cell carcinoma (BCC). This is especially true for women.
Unknown risk factors
It isn’t known whether or not the following factors are linked with non-melanoma skin cancer. It may be that researchers can’t show a definite link or that studies have had different results. Further study is needed to see if the following are risk factors for non-melanoma skin cancer:
- skin trauma
- eating unmodified dairy products such as whole milk, cheese and yogurt
- selenium supplements
Questions to ask your healthcare team
To make the decisions that are right for you, ask your healthcare team questions about risks.
Establishing a national caregivers strategy
The Canadian Cancer Society is actively lobbying the federal government to establish a national caregivers strategy to ensure there is more financial support for this important group of people.