It is estimated that more than two million cases of basal cell or squamous skin cancer (nonmelanoma) and 68,720 cases of malignant melanoma (the most serious form of skin cancer) were diagnosed in 2009 in the U.S.
Risk Factors for Skin Cancer
What Causes Basal and Squamous Cell Skin Cancer?
A risk factor is anything that affects a person's chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be controlled. Others, like a person's age or family history, can't be changed.
But risk factors don't tell us everything. Having a risk factor, or even many risk factors, does not mean that you will get the disease. And many people who get the disease may not have had any known risk factors. Even if a person with basal or squamous cell skin cancer has a risk factor, it is often very hard to know what part that risk factor may have played in getting the cancer.
These are risk factors for basal and squamous cell skin cancer:
Ultraviolet (UV) light
Sunlight is the main source of ultraviolet (UV) radiation, which can damage the genes in your skin cells. UV light is thought to be the major risk factor for most skin cancers. Tanning lamps and booths are another source of UV radiation. People with high levels of exposure to UV light are at greater risk for skin cancer.
The amount of UV exposure depends on the strength of the light, how long the skin was exposed, and whether the skin was covered with clothing and sunscreen. Many studies show that being exposed to a lot of sun when you are young is an added risk factor.
People who live in places with year-round, bright sunlight have a higher risk. For example, the risk of skin cancer is twice as high in Arizona compared to Minnesota. The highest rate of skin cancer in the world is in Australia. Spending a lot of time outdoors without covering your skin and using sunscreen increases your risk.
The risk of skin cancer is much higher for whites than for dark-skinned African Americans or Hispanics. This is because melanin helps protect against UV radiation. People with dark skin have more melanin. People with fair (light-colored) skin that freckles or burns easily are at extra high risk.
The risk of basal and squamous cell skin cancers goes up as people get older. Older people have been exposed to the sun for a longer time. Still, these cancers are now being seen in younger people too, probably because they are spending more time in the sun without protecting their skin.
Men are 2 times as likely as women to have basal cell cancers and about 3 times as likely to have squamous cell cancers of the skin. This could be because they spend more time in the sun.
Exposure to large amounts of arsenic increases the risk of skin cancer. Arsenic is a heavy metal used to make some insecticides. It is also found in well water in some areas. Workers exposed to industrial tar, coal, paraffin, and certain types of oil may have an increased risk, too.
People who have had radiation treatment have a higher risk of getting skin cancer in the area that was treated. This can be a problem for children who have had cancer treatment.
Having had a skin cancer
Anyone who has had one keratinocyte cancer has a much higher chance of having another one.
Certain long-term or severe skin problems
Scars from bad burns, areas of skin over bad bone infections, and skin damaged by certain skin diseases are more likely to develop skin cancer, but this risk is fairly small.
Some patients with psoriasis (a long-lasting inflammatory skin disease) are treated with psoralen and ultraviolet light treatments (PUVA). This can increase their risk of getting squamous cell skin cancer, and maybe other skin cancers, too.
Xeroderma pigmentosum: This very rare disease makes the skin less able to repair sun damage. This disease tends to run in families. People with this disease get many skin cancers, sometimes starting in childhood.
Basal cell nevus syndrome: This rare condition is present at birth. It causes some people to have many basal cell cancers. It often runs in families.
Weakened immune system
People with weak immune systems are more likely to develop non-melanoma skin cancer. For instance, people who have had an organ transplant often take medicines to weaken the immune system so that the body cannot reject the organ. These people are more likely to develop non-melanoma skin cancer. Skin cancers in people with weak immune systems tend to grow faster and are more likely to be fatal.
A small number of skin cancers seem to be linked to infection with human papilloma virus (HPV). This group of viruses can cause warts. The warts are different from the common type of warts that people get on their hands and feet. The HPV-related warts are often in the genital area and around the anus. They are linked to skin cancers in these areas.
Smoking is a risk factor for squamous cell skin cancer, but it is not a known risk for basal cell cancer.
Scientists have found that certain people are more likely than others to develop skin cancer after sun exposure. In these people, certain parts of the normal cells are more sensitive to being damaged by sunlight.
Source: American Cancer Society. (2010). Overview: Skin Cancer – Basal and Squamous Cell. Retrieved May 16, 2010, from http://www.cancer.org/docroot/CRI/CRI_2_1x.asp?rnav=criov&dt=51
What Causes Melanoma Skin Cancer?
We do not yet know exactly what causes melanoma skin cancer. But we do know that certain risk factors are linked to this disease. A risk factor is anything that affects your chance of getting a disease. Different cancers have different risk factors. Some risk factors, like smoking, can be controlled. Others, like a person's age or family history, can't be changed.
But risk factors don't tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have any known risk factors. Even if a person with melanoma has a risk factor, it is often very hard to know how much that risk factor may have contributed to the cancer.
Risk factors for melanoma skin cancer
UV (ultraviolet) light
Too much exposure to UV radiation is thought to be the biggest risk factor for most melanomas. The main source of UV light is the sun. Tanning lamps and booths are also sources of UV light. People with high levels of exposure to UV light are at greater risk for all types of skin cancer.
The amount of UV exposure depends on the strength of the light, how long the skin was exposed, and whether the skin was covered with clothing and sunscreen. Many studies have linked melanoma in the trunk, legs, and arms to frequent sunburns (especially in childhood).
A mole (the medical name is nevus) is a benign (not cancer) skin tumor. Certain types of moles increase a person's chance of getting melanoma. The chance of any single mole turning into cancer is very low. But a person who has many moles is more likely to develop melanoma. These people should have very thorough skin exams by a skin doctor (dermatologist). Many doctors suggest that they should also look at their own skin every month. Good sun protection is always important.
The risk of melanoma is more than 10 times higher for whites than for African Americans. Whites with fair skin, freckles, or red or blond hair have a higher risk of melanoma. Red-haired people have the highest risk.
Family history of melanoma
Around 10% of people with melanoma have a close relative (mother, father, brother, sister, child) with the disease. This could be because the family tends to spend more time in the sun, or because the family members have fair skin, or both. Less often, it is because of a gene change (mutation) along with sun exposure.
People with a strong family history of melanoma should do these things:
- Have regular skin exams by a skin doctor (dermatologist)
- Learn to look at their own skin and know what it should look like
- Be very careful about sun exposure
Having had melanoma in the past
A person who has already had melanoma has a higher risk of getting another one.
Weak immune systems
People who have been treated with medicines that suppress the immune system, such as transplant patients, have an increased risk of developing melanoma.
Melanoma is more likely to happen in older people. But it is a cancer that is also found in younger people. In fact, it is one of the most common cancers in people under 30.
In the US, men have a higher rate of melanoma than women.
Xeroderma pigmentosum (XP)
This is a rare, inherited condition. People with XP are less able to repair damage caused by sunlight and are at greater risk of melanoma and other skin cancers.
Source: American Cancer Society. (2009). Overview: Skin Cancer – Melanoma. Retrieved May 16, 2010, from http://www.cancer.org/docroot/CRI/CRI_2_1x.asp?rnav=criov&dt=39
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