What are the risk factors for basal and squamous cell skin cancers?

A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking and excess sun exposure, can be changed. 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 some people who get the disease may have few or no 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 how much that risk factor may have contributed to the cancer.

The following are known risk factors for basal cell and squamous cell carcinomas. (These factors don't necessarily apply to other forms of non-melanoma skin cancer, such as Kaposi sarcoma and cutaneous lymphoma.)

Ultraviolet (UV) light exposure

Ultraviolet (UV) radiation is thought to be the major risk factor for most skin cancers. Sunlight is the main source of UV rays, which can damage the DNA in your skin cells. Tanning beds are another source of UV rays. People who get a lot of exposure to light from these sources are at greater risk for skin cancer.

Ultraviolet radiation is divided into 3 wavelength ranges:

• UVA rays age cells and can damage cells’ DNA. They are mainly linked to long-term skin damage such as wrinkles, but are also thought to play a role in some skin cancers.
• UVB rays can directly damage DNA, and are the main cause of sunburns. They are also thought to cause most skin cancers.
• UVC rays don’t get through our atmosphere and therefore are not present in sunlight. They do not normally cause skin cancer.

While UVA and UVB rays make up only a very small portion of the sun’s rays, they are the main cause of the damaging effects of the sun on the skin. UV rays damage the DNA of skin cells. Skin cancers begin when this damage affects the DNA of genes that control skin cell growth. Both UVA and UVB rays damage skin and cause skin cancer. UVB rays are a more potent cause of at least some skin cancers, but based on what is known today, there are no safe UV rays.

The amount of UV exposure a person gets depends on the strength of the rays, the length of time the skin is exposed, and whether the skin is protected with clothing or sunscreen.

People who live in areas 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 for work or recreation without protective clothing and sunscreen increases your risk.

Many studies also point to exposure at a young age (for example, frequent sunburns during childhood) as an added risk factor.

Having light-colored skin

The risk of skin cancer is much higher for whites than for African Americans or Hispanics. This is due to the protective effect of the skin pigment melanin in people with darker skin. Whites with fair (light-colored) skin that freckles or burns easily are at especially high risk. This is one of the reasons for the high skin cancer rate in Australia, where much of the population descends from fair-skinned immigrants from the British Isles.

Albinism is a congenital (present at birth) lack of protective skin pigment. People with this condition may have pink-white skin and white hair. They have a high risk of getting skin cancer unless they are careful to protect their skin.

Older age

The risk of basal and squamous cell skin cancers rises as people get older. This is probably because of the buildup of sun exposure over time. These cancers are now being seen in younger people as well, probably because they are spending more time in the sun with their skin exposed.

Male gender

Men are about twice as likely as women to have basal cell cancers and about 3 times as likely to have squamous cell cancers of the skin. This is thought to be due mainly to higher levels of sun exposure.

Exposure to certain chemicals

Exposure to large amounts of arsenic increases the risk of developing non-melanoma skin cancer. Arsenic is a heavy metal found naturally in well water in some areas. It is also used in making some pesticides.

Workers exposed to industrial tar, coal, paraffin, and certain types of oil may also have an increased risk for non-melanoma skin cancer.

Radiation exposure

People who have had radiation treatment have a higher risk of developing skin cancer in the area that received the treatment. This is particularly a concern in children who have had radiation treatment for cancer.

Previous skin cancer

Anyone who has had a basal or squamous cell cancer has a much higher chance of developing another one.

Long-term or severe skin inflammation or injury

Scars from severe burns, areas of skin over severe bone infections, and skin damaged by some severe inflammatory skin diseases are more likely to develop skin cancers, although this risk is generally small.

Psoriasis treatment

Psoralens and ultraviolet light treatments (PUVA) given to some patients with psoriasis (a long-lasting inflammatory skin disease) can increase the risk of developing squamous cell skin cancer and probably other skin cancers also.

Xeroderma pigmentosum (XP)

This very rare inherited condition reduces the skin's ability to repair damage to DNA caused by sun exposure. People with this disorder often develop many skin cancers starting in childhood.

Basal cell nevus syndrome (Gorlin syndrome)

In this rare congenital (present at birth) condition, people develop many basal cell cancers over their lifetime. People with this syndrome may also have abnormalities of the jaw and other bones, eyes, and nervous tissue.

Most of the time this condition is inherited from a parent. In families with this syndrome, those affected often start to develop basal cell cancers as children or teens.

Reduced immunity

The immune system helps the body fight cancers of the skin and other organs. People with weakened immune systems (from certain diseases or medical treatments) are more likely to develop non-melanoma skin cancer, including squamous cell cancer and less common types such as Kaposi sarcoma and Merkel cell carcinoma.

For example, people who get organ transplants are usually given medicines that weaken their immune system to prevent their body from rejecting the new organ. This increases their risk of developing skin cancer. The rate of skin cancer in people who have had transplants can be as high as 70% within 20 years after the transplant. Skin cancers in people with weakened immune systems tend to grow faster and are more likely to be fatal.

Treatment with large doses of corticosteroid drugs can also depress the immune system. This may also increase a person's risk of skin cancer.

Human papilloma virus (HPV) infection

Human papilloma viruses (HPVs) are a group of more than 100 viruses that can cause papillomas, or warts. The warts that people commonly get on their hands and feet are not related to any form of cancer. But some of the HPV types, especially those that people get in their genital and anal area, seem to be related to skin cancers in these areas.

Smoking

People who smoke are more likely to develop squamous cell skin cancer, especially on the lips. Smoking is not a known risk factor for basal cell cancer.