What are environmental risk factors, and how can I avoid them?

Pollution coming out of factory stacks
When it comes to environmental factors that raise the risk of cancer, it may seem like avoiding exposure is as impossible as avoiding the air you breathe. In reality, though, you have more control than you think.

Tobacco smoke at a concert. Pollution from the factory around the corner. Radiation from a routine X-ray. When it comes to environmental factors that raise the risk of cancer, it may seem like avoiding exposure is as impossible as avoiding the air you breathe. In reality, though, you have more control than you think. Experts say you can lower your cancer risk simply by making strategic lifestyle changes or taking conscious measures to reduce your exposure. Environmental risk factors account for at least two-thirds of all cancer cases in the United States, so knowing more about what to look out for, and what to avoid, may go a long way in protecting your health.

Cancer develops when changes, or mutations, in a cell’s DNA cause the cell to grow out of control. Sometimes, the mutations are caused by chemicals and other toxic substances in the environment—classified as carcinogens because of their cancer-causing potential. While such chemicals are toxic, they don’t always cause cancer. Your risk for developing the disease depends on several factors—including how long and how often you’re exposed, your genetic makeup, your diet and lifestyle, your overall health, and your age and gender.

The International Agency for Research on Cancer (IARC) and the U.S. National Toxicology Program (NTP) group carcinogens into categories based on how likely they are to cause cancer. While most people think environmental cancer risks are strictly external toxins like air and water pollution and chemicals like radon, the IARC, NTP and others also count lifestyle factors like nutrition and tobacco use and natural exposures like ultraviolet light in the mix. Known environmental risk factors include:


The most significant environmental risk factor for cancer is tobacco, whether they’re using products like cigarettes, pipes, cigars, chewing tobacco, snuff or vaping, or being exposed to secondhand smoke. In fact, tobacco accounts for 80 percent to 90 percent of all cases of lung cancer, which is the second most common cancer in both men and women.

To reduce the risk of lung cancer, avoid tobacco altogether—don’t start the habit, and if you have, quit as soon as possible, and steer clear of secondhand smoke.


Research has found that the more alcohol someone drinks—especially regular use over time—the higher the risk of cancer. For example, people who have three-and-a-half drinks or more a day are two to three times more likely to develop head and neck cancer than those who don’t drink. Alcohol consumption also has been linked to liver, esophageal, colorectal and breast cancers.

Alcohol increases cancer risk by damaging cell DNA and proteins, as well as the body’s ability to break down nutrients, and by increasing estrogen levels. People who use both alcohol and tobacco have much higher risks of developing head and neck cancer than those who use alcohol or tobacco alone.


Obesity is linked to 13 types of cancer, including two of the most common—breast and prostate—but only a little more than half of Americans are aware that it’s a risk factor for cancer. In fact, physical inactivity and obesity together account for 25 percent to 30 percent of colorectal, breast, uterine, kidney and esophageal cancers, which are among the most common types. “Obesity has become so important in the field of oncology today that maintaining an appropriate weight is one of the most important ways you can protect yourself from cancer,” says Anthony Perre, MD, Chief of the Division of Outpatient Medicine at Cancer Treatment Centers of America® (CTCA).

To help avoid obesity-related cancers, experts recommend you lose excess weight through diet and exercise, if possible, and with the help of behavioral and dietary counseling, if necessary.

Ultraviolet radiation

Ultraviolet (UV) rays from the sun, sunlamps or tanning beds may damage cell DNA and lead to melanoma or other forms of skin cancer. Skin cancer is the most common form of cancer, affecting more than 3.5 million Americans each year, and melanoma accounts for the most skin cancer deaths. And its incidence is on the rise. In fact, if melanoma rates continue to increase at the same pace, 112,000 new cases of the disease will be diagnosed in 2030.

To reduce your risk, limit your exposure to UV rays—both from the sun and indoor tanning—and wear sunscreen and protective clothing when outdoors.


Asbestos occurs in rock and soil and is often found in building construction materials for insulation. The mineral fiber increases the risk of lung cancer, mesothelioma, laryngeal cancer and ovarian cancer. Asbestos exposure accounts for the largest percentage of occupational cancer risks, with the highest risk among affected workers who also smoke. The Occupational Safety and Health Administration regulates asbestos levels in workplaces, but because the fiber is present in the air, water and soil, avoiding asbestos is nearly impossible. Most people who are exposed to the fiber don’t develop disease, but the greater the exposure, the greater the risk.

If you are planning to remodel your home, which may disturb building materials, or if your home contains damaged materials, such as crumbling drywall or insulation, you may consider hiring someone to inspect it for asbestos-containing materials. If your home does contain asbestos, an inspector can give you recommendations for correction or prevention. And make sure to wear a mask and other protective gear while doing any of your own remodeling.


Certain viruses are linked to several types of cancer. Human papillomavirus (HPV), for instance, is responsible for almost all cervical cancers. But in November, a study published in The Annals of Internal Medicine journal found that HPV-related head and neck cancers in men (7.8 per 100,000) are even more prevalent than HPV-related cervical cancers in women (7.4 per 100,000).  The Centers for Disease Control and Prevention recommends that 11- and 12-year-old boys and girls receive two doses of the HPV vaccine six months apart, and that young men and women ages 15 to 26 receive three doses.

Chronic infection with hepatitis B or hepatitis C virus is the most common risk factor for liver cancer. Both viruses are spread by sharing contaminated needles, unprotected sex and childbirth. Also, the Epstein-Barr virus, which causes mononucleosis, is linked to some types of lymphoma. Currently, there are no vaccines for hepatitis C or Epstein-Barr, but there is a vaccine for hepatitis B.

Ionizing radiation

Ionizing radiation is thought to cause about 1 percent of all cancers. It comes from cosmic rays that enter the Earth’s atmosphere, the radioactive gas radon—found naturally at low levels in soil—and from certain medical procedures, such as X-rays and radiation therapy. When cancer treatments increase your risk of developing another cancer later in life, the decision-making process often involves weighing the risks against the benefits, says Glynis Vashi, MD, Intake Physician and Chief of Medicine at our hospital near Chicago. “It takes years for a cancer to develop,” she says. “So you do what you have to do at the time, and then you take as many preventive steps as possible to improve the chance that you won’t develop another cancer in the future.”

As medicine continues to evolve, scientists may discover more environmental substances that we should avoid, or at least limit in use. Today, some possible but unproven risk factors include fluoride in water, radiation from power lines and electrical devices, chemicals in certain hair dyes and cosmetics, lead, the mineral talc in talcum powder, diesel exhaust and the chemical BPA in some plastics. “My advice is to avoid or limit even these unproven risk factors now, especially if doing so doesn’t affect your quality of life,” Dr. Perre says.

The significance of environmental risk factors is underscored in cancer rate disparities throughout the world and how those rates fluctuate when people move from place to place. For example, people who live in Asia tend to have low rates of prostate and breast cancer and high rates of stomach cancer, but when they emigrate to the United States—where prostate and breast cancers are prevalent—their prostate and breast cancer rates rise over time.

Still, if everyone took all the known precautions in reducing environmental exposure to cancer-causing substances, some would still develop the disease—because environmental risk is only part of cancer’s story. For example, one man may smoke for 30 years and never develop lung cancer, while another who only smoked in college may develop the disease years later. “Many people believe that if they’re exposed to a carcinogen, they’ll get cancer,” Dr. Vashi says. “But you always have to question why, out of two people in the same environment, one will develop cancer and one will not. That is when you realize that there is something at play beyond the environment. It’s the interplay between the environment and what’s going on within us.”

Understanding the relationship between the environment and genetics is vital to lowering your cancer risk, Dr. Vashi says. “It’s education, education, education,” she says. “Every doctor should help his or her patient realize that a poor diet, excessive alcohol consumption and certain medications may affect chemical levels in the body that break down cancer-causing substances, for instance. It’s imperative that we help our patients learn how to decrease their environmental risks for cancer.” Researchers today are working to identify the unique combinations of gene alterations and environmental exposures that explain why one person develops cancer and another does not.

At the end of the day, you have the power to reduce potential exposures to substances in the environment, Dr. Hoag says. “I think the take-home point I would want to convey is that there may be a lot in your environment you can’t control, but the more you learn about what’s there, the more you learn about what you can control.”