- All cancers are a result of damage or genetic mutations in our DNA.
- But the many reasons individual cancer cases pop up in people are complex: Some are genetic and passed down from one generation to the next, and others are a result of things in our environment that we inhale, eat, or use.
- Visit Business Insider's homepage for more stories.
Cancer is the second-most-common cause of death in the United States, after heart disease.
It fundamentally affects the way our cells grow and divide, changing them in perverse ways. All cancer is a result of damage or genetic mutations in our DNA. The debilitating class of diseases spreads through a body like an invading army as toxic cells grow relentlessly into unruly tumors.
Some cases of cancer are out of our control, determined by genetic defects and predispositions passed down from one generation to the next, or spurred by genetic changes we undergo through our lifetime.
But we also know that breathing in certain substances, eating specific things, and even using some kinds of plastics ups the risk of developing some deadly cancers.
Here are some known carcinogens — cancer-causers — and a few more things that scientists are zeroing in on as prime suspects.
Scientists now know that eating too much sweet stuff can not only lead to diabetes but actively damage your cells and increase your risk of developing cancer. But that's not all.
New research suggests that sugar may fuel tumor growth in the body because cancer loves to use sugar as fuel.
"The hyperactive sugar consumption of cancerous cells leads to a vicious cycle of continued stimulation of cancer development and growth" Johan Thevelein, a Belgian molecular biologist, said in October after the release of his study.
Scientists say that the groundbreaking research gives us a better understanding of how sugar and cancer interact and that it could one day help create targeted diet strategies for patients.
Any food that comes in a crinkly plastic wrapper, is industrially sealed, and is designed to last for months without spoiling may be a quick on-the-go fix for a hunger pang, but it's also likely increasing your risk of cancer.
Scientists in France recently zeroed in on a link between people who eat more processed foods and those who develop cancer.
They're not sure yet whether the problem is the shelf-stabilizing ingredients, the plastic packaging, or some combination of the two. And because their study was correlative, it's possible there's some other hidden factor at work.
Though the tobacco industry tried to cover this one up, we've known for years that tobacco smoke contains at least 70 cancer-causing chemicals.
And it's not just smokers who are affected: People who inhale secondhand smoke can develop deadly forms of cancer too.
The Centers for Disease Control and Prevention says: "Nonsmokers who are exposed to secondhand smoke at home or at work increase their risk of developing lung cancer by 20-30%."
People who chew tobacco are at increased risk, too.
Tanning and unprotected sun exposure
According to the Skin Cancer Foundation, people who use a tanning bed before age 35 increase their risk of developing melanoma by 75%.
Regular sun can hurt you, too, so wearing protective clothing and sunscreen and finding shade are good ideas if you're going to be out in the sunshine for more than 15 minutes.
Toxic chemicals at work
Some people work with cancer-causing substances every day.
Those at risk of coming in contact with cancer-causing substances on the job include:
• aluminum workers
• tar pavers (who come in contact with the carcinogen benzene)
• rubber manufacturers
• hairdressers who deal with dyes daily
• nail-salon workers breathing in dangerous fumes
The night shift
The International Agency for Research on Cancer in 2007 classified nighttime work as a probable carcinogen. Scientists think working at night and working long hours into the darkness can each mess with the body's natural circadian sleep and wake cycles.
The CDC has a full list of occupational cancer hazards.
Arsenic, a natural part of the Earth's crust, is toxic in its inorganic form. It's often found in contaminated drinking water in places like Bangladesh, or in spots where irrigation systems for crops use arsenic water.
The World Health Organization says at least 140 million people in 50 countries drink water containing high levels of arsenic. (It's also one of the cancer-causing agents in tobacco.)
Charred meat and grilling over an open flame
Smoky meats from the grill may be tender and tasty, but they probably also increase your risk of cancer. That's because the muscle meats contain compounds called heterocyclic amines, or HCAs, and polycyclic aromatic hydrocarbons, or PAHs.
According to the National Cancer Institute, when meats like beef, poultry, or fish are cooked over a hot open flame or pan-fried at high temperatures, the fat and juices they release into the fire spark flames with the dangerous chemicals inside that then cook into the meat we eat.
They're not positive that these chemicals cause cancer, but in lab tests they have been found to change DNA in ways that might increase the risk of cancer.
Coal miners have for years had higher rates of cancer in their lungs, bladder, and stomach. There's sufficient data to suggest miners who deal with coal gasification or who inhale coal dust can get cancer.
Regular heavy alcohol consumption can up your risk of developing several different kinds of cancer, including throat, liver, breast, and colon cancer.
According to the National Cancer Institute, "the risk of developing cancer increases with the amount of alcohol a person drinks."
A new analysis of nearly 600,000 drinkers in 19 high-income countries found that drinking more alcohol is associated with developing all kinds of cancers of the digestive system. Another recent study of alcohol consumers in 195 countries and territories around the world found that more than one in four alcohol-related deaths in people over age 50 are due to cancer.
Diesel oil has more than 30 components that can cause cancer, according to the International Agency for Research on Cancer.
Salt-cured meat or fish and pickled foods
Salt-cured fish, which is popular in China, is high in nitrates and nitrites, known carcinogens in animals that may also cause cancer in humans. The chemical compounds can damage DNA, leading to head and neck cancer.
According to Cancer Research UK, "people from China, or with Chinese ancestry living in the UK, have higher rates of nasopharyngeal cancer than other ethnic groups," something that might be because of their diet.
Eating lots of pickled foods can also increase your risk of stomach cancer.
Chemicals used in oil fracking that may be released into air and water include the cancer-causers benzene and formaldehyde.
Processed meats like ham, bacon, and sausage
The World Health Organization says processed meats like hot dogs, ham, bacon, and sausage can contribute to cancer risk. That's because the meat has been treated in some way to preserve or flavor it, such as by salting, curing, fermenting, or smoking.
WHO says it's possible that any kind of red meat could be linked to an increased risk of colorectal cancer, and there's some evidence to suggest the meat also contributes to pancreatic and prostate cancers, though that evidence is not as strong.
A recent roundup of 15 breast-cancer studies found that people who regularly eat more processed meats increase their risk of developing breast cancer by 9%, when compared to people who don't eat very much processed meat at all.
Consuming the equivalent of one hot dog or roughly two slices of bacon every day increases your relative risk for colorectal cancer by 18%.
Asbestos was used as an insulation material for years before the dust was linked to lung cancer.
Products that contain asbestos are not completely banned in the US, though the Environmental Protection Agency regulates their use.
Glyphosate, a common weed killer used by many farmers
You may know the chemical better as an active ingredient in Monsanto's Roundup.
A group of more than 300 US farmers sued Monsanto in federal court earlier this year, alleging that working with the chemical has given them cancer. In May, a jury in California ordered Monsanto to pay over $2 billion to a couple who claimed that using Roundup for 35 years caused them to contract non-Hodgkin lymphoma, following another $80 million payout a judge awarded last year to a school groundskeeper who used the weed-killer up to 30 times per year.
Monsanto argues there's no evidence the chemical causes cancer and points to one 2017 study of more than 54,000 pesticide sprayers in Iowa and North Carolina that found no statistically significant association between glyphosate and any kind of cancer.
But that study did say that chemical sprayers who had the most exposure to the chemical were more at-risk of developing acute myeloid leukemia than others.
Scientists are still not sure there's enough evidence that the trace amounts of the pesticide found in food is harmful to our DNA, but more and more research suggests it's not good for people who are exposed to the chemical day after day, such as farmers and gardeners. It's also definitely killing off some butterflies.
Saw-mill workers and cabinetmakers who breathe in lots of dust from cutting and shaping wood regularly are more likely to develop cancers of the sinus and nasal cavity than the average person.
Birth control and estrogens
Women who start menstruation early or go into menopause later may have an increased risk of breast cancer because they're exposed to more estrogen and progesterone made by the ovaries.
Women going through menopause who use a combined estrogen-progestin therapy to help ease their symptoms may also be at a greater risk of developing breast cancer.
Using birth-control pills may also increase a woman's risk of developing cervical cancer, though there is some evidence that being on birth control is associated with a reduced risk of developing other cancers, such as endometrial (uterus), colorectal, and ovarian.
Catching certain kinds of viruses can indirectly increase your risk of cancer. That's because, in some situations, viruses trigger genetic changes in cells that can contribute to cancer.
The CDC: "Some viruses linked to cancer are the human papillomavirus (HPV), which causes cervical cancer; hepatitis B and C viruses, which can cause liver cancer; and the Epstein-Barr virus, which may cause a type of lymphoma. Also, the H. pylori bacterium can cause gastric cancer."
Some cancer risk is passed down from one generation to the next. Genetic mutations play a key role in about 5% to 10% of all cancers.
"Genetic changes that promote cancer can be inherited from our parents if the changes are present in germ cells, which are the reproductive cells of the body (eggs and sperm)," the National Cancer Institute says.
For example, certain kinds of breast cancer are a result of mutations in the BRCA1 and BRCA2 genes.
Obesity can put you at increased risk of developing types of cancers including breast, colon, rectum, esophagus, kidney, and pancreas.
But there are things you can do to reduce your risk. Prevention includes eating healthy foods and getting enough physical activity, both of which not only help people maintain a healthy weight and reduce their chances of developing some of those cancers but can ward off depression and boost your mood.
Scientists have known for years that formaldehyde can cause nasal cancer in rats.
The preserving agent and disinfectant is used in some glues and building products, and the International Agency for Research on Cancer says it can cause cancer in humans too.
Putting foreign objects into your body like silicone breast implants (or other metals and ceramics) can lead to cancer, according to the International Agency for Research on Cancer.
But the Mayo Clinic says the find isn't a reason to put your surgeon on speed dial just yet.
"A recent review of documented cases of BIA-ALCL (breast implant-associated anaplastic large cell lymphoma) in the United States from 1996 to 2015 determined that the incidence of BIA-ALCL was two per 1 million women with a textured breast implant," according to Mayo.
Smoggy air, and the particulates in it, can also lead to cancer.
Soot in general isn't great. In London, people started noticing lots of chimney sweeps developing scrotal cancer in the 1770s, and further studies found a link between the backbreaking chimney work and higher cancer rates.
Soot inhalation has also been linked to lung, esophageal, and bladder cancers.
Breathing air infused with toxic fumes for years at a time can lead to cancer.
Scientists have studied New York City firefighters, office workers, and students who returned to downtown Manhattan in the days and weeks after the 9/11 attacks and found that they consistently have higher rates of roughly 70 different types of cancer, including breast, cervical, colon, and lung cancers.
According to the federal World Trade Center Health Program count, more than 9,300 firefighters, cops, office workers, and children who were living in or working around downtown Manhattan on 9/11 have cancer. An additional 420 survivors have died from cancer.
Likewise, people who lived near the site of the 1986 nuclear disaster at Chernobyl in Ukraine have developed higher-than-usual rates of lung and thyroid cancers as well as leukemia.
Silica is a natural mineral found in sand, stone, and concrete. When construction workers and miners inhale silica particles by cutting, sawing or drilling into rock, it can increase their risk of developing lung cancer.
But one trip to the doctor isn't going to give you cancer.
The link between radiation and cancer risk tends to show up in studies of people who've been exposed to high doses of radiation, like people affected by the Chernobyl nuclear accident, and people who have cancer, who are sometimes treated with high doses of radiation.
Still, the American Cancer Society cautions that "there is no threshold below which this kind of radiation is thought to be totally safe."
Chronic, long-term, DNA-damaging inflammation
Chronic inflammation from things like long-term infections, bowel disease, or obesity can all damage a person's DNA and lead to higher cancer rates.
Plastics can be dangerous, especially when they leach chemicals out through scratches or cracks in a container.
BPA is a synthetic estrogen that has been used in many plastics and resins since the 1960s. BPA resins can be used inside products like metal food cans as sealants, while polycarbonate BPA plastics can include water bottles and food storage containers.
BPA even shows up on the shiny side of receipt paper to stabilize the ink.
While many plastics manufacturers have started labeling their products "BPA-free," there's still a lot of the breast- and prostate-cancer-causing stuff around.
Getting intimate before you've had your HPV shots
Human papillomavirus is a common family of sexually transmitted viruses, and it's one of the ones we mentioned earlier that can cause cancer. The Centers for Disease Control and Prevention says more than 40 different types can be passed through sexual contact.
Many forms of the virus go away on their own and are relatively harmless, but others can cause cervical, penile, vaginal, and anal cancers. Even using a condom won't necessarily prevent the spread of HPV, though. That's why the CDC recommends that all boys and girls get the HPV vaccine, ideally before their first sexual encounter.
And, in rare cases, a smooch can cause cancer
About 98% of us will contract the potentially cancer-causing mononucleosis virus by the time we're adults, from kissing someone who has the virus, sharing food or drinks, or coming in close contact with them when they're coughing or sneezing.
This Epstein-Barr virus is relatively harmless for most of us, but in rare cases the herpes can lead to higher rates of nose cancers, lymphomas, and stomach cancers.
Scalding hot beverages that can burn your tongue
Drinking scalding hot beverages that are steamy enough to burn a person's tongue prompts more cases of throat cancer.
Scientists have discovered that people who drink super-hot maté, traditionally served piping hot in chilly areas of South America, do have some higher rates of esophageal cancer, and drinking alcohol and smoking can compound the risk.
Recently, researchers also discovered that people in northeastern Iran who drank two cups of very hot tea every day were at a 90% higher risk of developing esophageal cancer than their Iranian neighbors who waited for their brew to chill.
This cancer risk is relatively small, though, and also fairly easy to avoid. Be kind to your tongue and to your esophagus: Wait a few minutes before you sip hot drinks.
The browning of some foods that are cooked at high temperatures — like bread, coffee, or french fries — produces a chemical compound called acrylamide. It happens naturally in a process called the Maillard reaction.
The dose of acrylamide in a toasty cup of coffee or a chewy cookie is probably not going to kill you. It's dangerous when consumed in large doses, and it's one of the toxic chemicals smokers inhale, but there's no evidence that a little browning is harmful.
A California judged ruled in 2018 that coffee sellers in that state must include labels warning their customers about the possible cancer risks from acrylamide in coffee. But state and federal health experts aren't convinced the new rule is based on the best science.
The California Office of Environmental Health Hazard Assessment (OEHHA) is challenging the law, arguing there's not enough evidence that coffee causes cancer. The US Food and Drug Administration agrees, and recently backed up OEHHA's assessment, saying a cancer warning on coffee is more likely to confuse and mislead consumers than help them out.
In fact, both the International Agency for Research on Cancer and the American Cancer Society say scientific research suggests coffee is more likely a cancer fighter, as it can reduce people's risk of developing certain cancers in the breast, liver, and colon
Acrylamide is just one of more than 1,000 chemicals on a list that the state of California has on its danger list of potentially cancer-causing compounds. By law, California puts cancer warnings on all kinds of things, from parking decks to dentists' chairs.
While it is true that what we eat, where we go, and the things we breathe in every day can contribute to our chances of developing certain types of cancer, it's important to remember the class of debilitating and deadly diseases is not yet fully understood, and scientists are still hunting for cancer cures.
Update: This story has been updated to reflect the most recent studies on the chemical glyphosate, and the ongoing lawsuits against Monsanto.