What Does Cytotoxic Mean?

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Cytotoxic means that a substance or process can damage cells or cause them to die. "Cyto" means cell and "toxic" means poison.

You might hear the word when talking about chemotherapy drugs that kill cancer cells. It can also describe other toxins like venom from snakes. The human immune system even has cells that are cytotoxic: T-cells kill bacteria, viruses, and cancer cells.

This article will go over the different types of cytotoxic substances. You will also learn how to protect yourself from something that is cytotoxic.

Hand in latex glove holding IV system containing cytotoxic chemotherapy

Cytotoxic Drugs

An example of a cytotoxic medication is chemotherapy, which acts on cancer cells. The drugs work on cells that are growing very fast. Cancer cells, hair follicles, bone marrow, and cells in the stomach and intestines are examples of rapidly-growing cells.

Cytotoxic drugs interrupt cells at certain places in the growth cycle. Since cells are in different places in the division process, they can't all be killed at once. That's why chemotherapy regimens usually include a combination of drugs and the cycles of treatment have to be repeated.

Cytotoxic v. Cytostatic

While the names look similar, a cytotoxic agent is different from a cytostatic one. Cytostatic medications stop cell division and growth but do not directly cause cells to die.

Chemotherapy drugs are made to kill all the cells that are growing fast—even normal cells. However, not all drugs that treat cancer are cytotoxic.

New treatments like targeted therapies and immunotherapies are not cytotoxic. Instead, they work by getting in the way of a cancer cell's growth. They can also use the immune system to fight cancerous cells.

There are some immunotherapies that are considered somewhat cytotoxic because they take advantage of the cell-destroying actions of the body's own T-cells. An example of this type of treatment is CAR-T therapy.

Cytotoxic Agents in Humans and Animals

Cytotoxic substances can also be found in humans and animals.

Cytotoxic T-cells

Our bodies make cytotoxic T-cells, also called cytotoxic T-lymphocytes. These types of T-cells, search for, find, and destroy cells that are infected by viruses. They can also kill cancer cells.

One exciting area of cancer research is focused on using the body's own cytotoxic cells to fight cancer. For example, CD8+ cells and natural killer lymphocytes are the immune system's own cytotoxic cells.

These treatments work in different ways. Some help T-cells "see" cancer cells that were previously hidden, while others harvest and make more of the cells.

Cytotoxic Venom

Humans are not the only creatures that have cytotoxic T-cells. For example, venoms found in vipers, cobras, and violin spiders are cytotoxic.


Cytotoxic substances are harmful to cells. Cytotoxic medications, like chemotherapy drugs, are made to kill cancer cells or keep them from growing. Other cytotoxic substances are found in nature, like venom from some snakes.

Your body even produces its own cytotoxic cells that are a key player in your immune system.

Mechanism of Action

Cytotoxic agents can kill cells in a few ways. An agent may weaken a cell's membrane, which usually makes the cell explode (called lysis). Some agents make cells stop growing and dividing.

There are also agents that work on the DNA inside cells. These are genotoxic, rather than cytotoxic, substances.

Cytotoxic vs. Genotoxic

It's easy to confuse the terms "cytotoxic" and "genotoxic." Cytotoxic means a substance causes damage to cells. Genotoxic means a substance directly damages the DNA in cells.

When DNA is damaged, it may or may not die. A cell with damaged DNA is said to have mutations. If the mutated cells don't get fixed, it can lead to cancer.

Cancer often happens when there are mutations in two kinds of genes:

  • The genes that code for proteins that drive the growth of cells (oncogenes)
  • The genes that code for the proteins that fix damaged DNA or cause a cell to die if the DNA cannot be fixed (tumor suppressor genes) The BRCA genes are an example of this kind of gene.

Carcinogenicity and Mutagenicity 

To understand cytotoxicity, there are two other important words to know: carcinogenic and mutagenic.

  • A carcinogen is a cytotoxic substance that has the ability to cause DNA damage that could ultimately lead to cancer.
  • If something is mutagenic, it is a cytotoxic substance that could potentially damage the chromosomes or genes in a fetus.

The risks of cancer and the potential effects on a developing fetus are why it's important that people handle cytotoxic substances very carefully.


Cytotoxic drugs can kill cells or stop them from growing and dividing. Genotoxic drugs cause damage to the DNA inside the cells.

Carcinogens damage DNA in cells. This causes mutations that can lead to cancer. Mutagenic substances can harm the genes in a developing fetus.

Dangers of Cytotoxic Substances

Cytotoxic drugs kill cancer cells but they can also damage normal, healthy cells. Many of the side effects from chemotherapy are related to this process.

Taking Precautions

People who work with cytotoxic medications or substances need to be very careful. The specific steps they need to take depend on how they might be exposed to a substance.

Precautions a person might need to take when handling cytotoxic substances include:

  • Gloves with their shirt cuffs tucked under the gloves
  • Long sleeve clothing
  • Disposable gowns
  • Safety glasses
  • Respiratory protection

Patients going through cancer treatment may need to take cytotoxic precautions when they go home. These measures protect their family members who could be accidentally exposed to body fluids that have cytotoxic chemicals in them.

Cytotoxicity Testing

Cytotoxicity testing helps people stay safe where they live and work. It also helps companies make sure that products like medical devices are safe. If something is labeled cytotoxic, a person will know that they need to take precautions when they are handling it.

Many manufacturers use cytotoxicity testing, including those that make drugs and cosmetics. Plant products used for extracts are also tested for toxicity.


People who handle cytotoxic substances need to be very careful. There are steps they can take to stay safe, like wearing gloves and gear that protect them from the substances.

People getting chemotherapy may need to take precautions to avoid accidentally exposing people around them to the cytotoxic medicines they are taking.


Cytotoxic substances damage or kill cells. Medications like chemotherapy are cytotoxic. The venom produced by some animals can be cytotoxic. Even some of the cells in your body are considered cytotoxic.

People who have to handle cytotoxic substances need to be very careful. Since these substances harm cells, they can increase the risk of cancer. They can also have negative effects on a fetus.

A Word From Verywell

The word "cytotoxic" can look scary—especially if you see the label on medicine you need to take. The word means that a substance can damage or kill cells. However, these substances also occur in nature. Your body even makes its own cytotoxic substances that help your immune system fight.

It's important to understand how cytotoxic substances work because they are dangerous. If you handle them, you need to take precautions to protect yourself and the environment from their harsh effects.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."