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. The most important risk factor for non-melanoma skin cancer is ultraviolet radiation (UVR) from the sun and indoor tanning.
Non-melanoma skin cancer is the most common cancer diagnosed in Canadians. It makes up at least 40% of all new cancer cases in Canada.
Statistics for non-melanoma skin cancers show that the chance of developing non-melanoma skin cancer increases with age. Most new cases are diagnosed in people between 80 and 90 years of age. But most cancer registries in Canada do not collect information about non-melanoma skin cancers. This is because these cancers are hard to keep track of. The information often doesn’t get reported because non-melanoma skin cancer is usually diagnosed and treated easily in a doctor’s office.
Of the most common types of non-melanoma skin cancer, basal cell carcinoma (BCC) seems to affect men and women equally, and squamous cell carcinoma (SCC) is diagnosed more often in men.
Actinic keratosis is a precancerous condition of the skin. It isn’t cancer, but it can sometimes become SCC if it isn’t treated. Some of the risk factors for non-melanoma skin cancer may also cause actinic keratosis. Find out more about actinic keratosis.
Risk factors are generally listed in order from most to least important. But in most cases, it is impossible to rank them with absolute certainty.
There is convincing evidence that the following factors increase your risk for non-melanoma skin cancer.
Being in contact with ultraviolet radiation (UVR) is the most important risk factor for developing skin cancer. The sun is the main source of UVR. Indoor tanning equipment, such as tanning beds and sun lamps, is also a source of UVR.
Having a tan means that your skin has been damaged by contact with UVR. UVR can cause sunburns, premature aging, cataracts and skin cancers.
Most cases of non-melanoma skin cancer are caused by contact with UVR from the sun over a long time. People who work outside, such as farmers, have a higher risk of developing non-melanoma skin cancer because they are outdoors for long periods. People who live at high altitudes or in areas with year-round, bright sunlight also have a greater risk of developing non-melanoma skin cancer.
BCC is most common in people with a fair complexion. It has been most strongly linked to on-and-off exposure to UVR, sunburns and overexposure during the childhood or teenage years.
SCC is most strongly linked to total lifetime sun exposure. This includes recreational and work-related exposure and being exposed to UVR a lot during childhood.
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 a 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 skin cancer (non-melanoma or melanoma) have a greater risk of developing another skin cancer, including BCC and SCC.
People who had radiation therapy (a source of ionizing radiation) have a greater risk of developing non-melanoma skin cancer in the treatment area. This type of skin cancer can develop 15 to 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.
Coming into contact with arsenic increases the risk of developing non-melanoma skin cancer. Arsenic is a naturally occurring substance found in rocks and soil. Arsenic and substances 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 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.
Working with certain 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 therapy is a treatment used for skin conditions such as psoriasis. It uses the drug psoralen and UVA radiation. Psoralen makes the skin more sensitive to UVA light. Receiving PUVA therapy for a long time increases your risk of developing SCC.
Xeroderma pigmentosum is a hereditary condition that affects the skin so it can’t repair sun damage. When someone has xeroderma pigmentosum, their skin is more sensitive to UVR so that it changes colour and ages prematurely. People with xeroderma pigmentosum also have a high risk of developing non-melanoma and melanoma skin cancers.
Basal cell nevus syndrome is also known as Gorlin syndrome or nevoid basal cell carcinoma syndrome. It is a rare hereditary 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. This includes people who had an organ transplant and must take medicines to suppress their immune system and those infected with the human immunodeficiency virus (HIV).
Possible risk factors
The following factors have been linked with non-melanoma skin cancer, but there is not enough evidence to show for sure that they are risk factors. More research is needed to clarify the role of these factors for non-melanoma skin cancer.
- human papillomavirus (HPV) infection
- taking medicines that make your skin more sensitive to the sun (called photosensitizing drugs)
- having lots of freckles or moles
- smoking tobacco
Questions to ask your healthcare team
To make the decisions that are right for you, ask your healthcare team questions about risks.
A type of high-energy radiation that can remove particles from an atom or molecule resulting in charged ions. These charged ions can cause changes to cells’ DNA that can damage or kill the cells. This can increase the risk of cancer.
Ionizing radiation is present in the atmosphere. It can also come from medical tests or treatments, such as x-rays or radiation therapy.
Passed from parent to child through information contained in genes.
Also referred to as hereditary.
A type of virus that causes abnormal tissue growth (warts) and other changes to cells.
There are over 100 types of HPV. Most types of HPV cause harmless warts on the hands, fingers, feet and even the face. Some types of HPV cause genital warts, are associated with an increased risk of several different types of cancer, including cancers of the cervix, oropharynx, anus, penis and vulva.
A non-cancerous (benign) growth on the skin that is usually tan, brown or flesh-coloured.
Moles are made up of a cluster of melanocytes (cells that make melanin, which gives skin, hair and eyes their colour). They may be raised or flat.
Also called nevus.
What’s the lifetime risk of getting cancer?
The latest Canadian Cancer Statistics report shows about half of Canadians are expected to be diagnosed with cancer in their lifetime.