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Cancer is a very complex disease. It happens when DNA mutations occur that cause cells in your body to grow and divide out of control.

Carcinogens are substances that can cause DNA changes that may lead to cancer.

This article will take a closer look at carcinogens, how they can cause cancer, and the steps you can take to help protect yourself from known carcinogens.

A carcinogen is a substance or type of exposure that can cause cancer to develop.

You can encounter carcinogens in many different forms. This includes through:

  • the environment
  • specific lifestyle choices
  • certain medical treatments
  • some types of infections
  • exposure at home or in the workplace

Scientists use laboratory studies in cells and animals to help determine if a specific substance is a carcinogen. They also use epidemiological studies, which evaluate trends and risk factors associated with cancer in a set group of people.

How are carcinogens classified?

Two organizations mainly determine which agents are considered carcinogens. These are the International Agency for Research on Cancer (IARC) and the National Toxicology Program (NTP).

The IARC, which is part of the World Health Organization (WHO), has reviewed over 1,000 potential carcinogens. However, only 122 agents are currently classified as known carcinogens to humans. The rest are classified as:

  • probably carcinogenic (93 agents)
  • possibly carcinogenic (319 agents)
  • not classifiable — unknown risk (501 agents)

The NTP is made up of parts of several government agencies in the United States, including:

  • the National Institutes of Health (NIH)
  • the Food and Drug Administration (FDA)
  • the Centers for Disease Control and Prevention (CDC)

The NTP updates their report on carcinogens every few years. The most recent update was in December 2021. Currently, 64 agents are listed as known carcinogens to humans while 192 are anticipated to be carcinogens to humans.

The discrepancy in the number of classified carcinogens isn’t because these agencies disagree on what’s a carcinogen and what’s not. It’s simply because both agencies haven’t yet analyzed the data on the same substances.

Cancer happens due to mutations (changes) in DNA. These mutations impact the way some cells grow and divide in your body.

Normally, cell growth and division is a tightly controlled and very precise process. But when this process becomes disrupted, it can cause cells to grow and divide in an uncontrolled and unpredictable way.

Cell mutations that may lead to cancer can:

  • be inherited from your parents
  • happen over time due to natural errors during DNA replication, a process that needs to take place each time a cell divides
  • happen due to carcinogens that you encounter during your lifetime

Simply put, carcinogens cause damage to DNA. In most cases this damage is caught and repaired by specialized proteins in your cells. In severe situations, the affected cell may even die.

However, sometimes these safeguards don’t happen. When DNA damage in a cell isn’t repaired, it can lead to mutations that can contribute to the development of cancer.

However, just because something is labeled as a carcinogen doesn’t mean it will absolutely lead to cancer. The risk of being exposed to a certain carcinogen can be influenced by many factors, including:

  • the specific carcinogen in question
  • the frequency of exposure (how often)
  • the intensity of exposure (how much)
  • the length of exposure (how long)
  • individual genetic factors

Some types of cancer appear to have “windows of susceptibility.” This means that some people may be more likely to develop cancer at specific times of their life (for instance during puberty or menopause) than at other stages.

There are many different types of carcinogens. Let’s look at some of the most common ones.

Lifestyle-related carcinogens

Lifestyle-related carcinogens are tied to circumstances or choices associated with your day-to-day life. Some of the most common lifestyle-related carcinogens that you may be familiar with include:

According to the American Cancer Society (ACS), tobacco is the leading cause of preventable death in the United States. It causes 20% of all cancers, including 80% of lung cancers, and about 30% of all cancer deaths.

Environmental carcinogens

Some environmental carcinogens, such as UV radiation or radon, may occur naturally. Others, like secondhand smoke and air pollution, are human-made.

Examples of common environmental carcinogens include:

  • UV radiation from sunlight
  • secondhand smoke that you breathe in from people who are smoking tobacco products
  • thirdhand smoke, which is the long-lasting residual smoke that’s left on surfaces (like clothing and furniture) from tobacco products

The American Academy of Dermatology (AAD) notes that skin cancer is the most common cancer in the United States, with about 1 in 5 people developing it at some point in their lifetime.

This includes cancers that are malignant (cancerous) as well as noninvasive carcinomas that can be surgically removed. Exposure to excess UV light is the main risk factor for all types of skin cancer.

Medical-related carcinogens

Medical-related carcinogens include some types of infectious agents, such as viruses and bacteria, as well as specific types of drugs and medical treatments.

Infectious agents that may increase the risk of cancer include:

A 2019 study estimated that 2.2 million new cancer diagnoses worldwide were caused by infections in 2018. The main causes included H. pylori, HPV, and hepatitis B and C.

Some examples of medical treatments that are known carcinogens include:

Occupational carcinogens

Occupational carcinogens are those that you may be exposed to on the job. Some occupations can put you at increased risk of prolonged exposure to high levels of carcinogens. These include jobs in:

  • agriculture
  • construction
  • mining
  • metalworking
  • painting
  • rubber or plastic manufacturing

Some examples of occupational carcinogens include:

A 2021 study used data on occupational carcinogens collected from 195 countries between 1990 and 2017. It found that:

  • There were 319,000 deaths associated with occupational carcinogens in 2017.
  • Occupational carcinogen exposure levels have decreased overall, but cancer burden has increased, likely due to past exposures.
  • Most occupational carcinogens cause cancers of the respiratory tract.
  • Asbestos and silica exposure have accounted for much of the occupation-associated cancers over the past 20 years.

There’s no surefire way to prevent cancer. However, there are ways to limit your exposure to carcinogens. To reduce your exposure to known carcinogens, you can take the following key steps:

  • If you smoke, consider quitting smoking. This includes cigarettes, cigars, and smokeless tobacco products.
  • Try to avoid exposure to secondhand smoke whenever possible.
  • Consume alcohol in moderation or not at all.
  • Limit your intake of processed meats.
  • Apply sunscreen before spending time out in the sun.
  • Refrain from using tanning beds.
  • Try to stay inside when the air quality is bad and use air filters in your home to reduce air pollution.
  • Test your home’s radon levels if they’ve never been tested or are unknown.
  • Stay up-to-date on all recommended vaccinations, particularly those for hepatitis B and HPV.
  • Take steps to prevent developing infections caused by viruses like HIV and HCV by using barrier methods during sex and not sharing injection drug equipment.
  • Use appropriate personal protective equipment if you work in an occupation where you may be regularly exposed to carcinogens.

Some medical treatments are considered carcinogens. However, in many cases, the benefits of these treatments outweigh the potential risks. It’s always important to discuss the benefits and risks of any new medical treatment with your doctor.

Carcinogens are substances or exposures that can increase the risk of cancer development. These substances have the potential to cause damage to your DNA which, in turn, can impact the way some cells grow and divide in your body. When cells grow and divide out of control it can result in cancer development.

There are many types of carcinogens. Some are linked to your lifestyle or occupation. Others are present in the environment or are associated with infections or medical treatments.

There’s no way to prevent cancer completely. However, you can take steps to avoid exposure to known carcinogens, which may help reduce your risk of developing cancer.