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 several 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.

The following 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 too much 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 at a young age 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 wearing enough clothing and sunscreen increases your risk.

Fair skin

The risk of skin cancer is much higher for whites than for dark-skinned African Americans. 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.

Older age

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 period of time. Still, these cancers are now being seen in younger people too, probably because they are spending more time in the sun with their skin exposed.

Men

Men are 2 times as likely as women to have basal cell cancers and 3 times as likely to have squamous cell cancers of the skin. This could be because they spend more time in the sun.

Chemicals

Exposure to large amounts of arsenic, a heavy metal used to make some insecticides, increases the risk of skin cancer. Workers exposed to industrial tar, coal, paraffin, and certain types of oil may also have an increased risk.

Radiation

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. Almost all of these cancers are basal cell.

Having had a skin cancer

Anyone who has had one skin cancer has a much higher chance of having another one.

Certain long-term or severe skin problems

Scars from severe burns, areas of skin over severe bone infections, and skin damaged by certain skin diseases are more likely to develop skin cancer, but this risk is fairly small.

Treatment of psoriasis

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.

Skin disease

A very rare disease called xeroderma pigmentosum 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 weakened immune systems are more likely to develop non-melanoma skin cancer. For example, people who have had an organ transplant often take medicines to weaken the immune system in order to keep the body from rejecting the organ. These people are more likely to develop non-melanoma skin cancer. Skin cancers in people with weakened immune systems grow much faster and are more likely to be fatal.

HPV infection

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

Smoking is a risk factor for squamous cell skin cancer but not for basal cell cancer.

Genetics

Scientists have found that certain people are more likely than others to develop skin cancer after sun exposure. In these people, the parts of the normal cells are more sensitive to being damaged by sunlight.