When one hears the word cytotoxicity, it might sound familiar but unclear, or it may even sound intimidating. But at its core, cytotoxicity simply refers to the ability of something to harm or kill cells¹⁻⁴.

As health care professionals caring for individuals experiencing skin or wound related challenges, understanding cytotoxicity is crucial. This is particularly true as new medical materials and treatments enter clinical use. Even for patients and caregivers, knowing about cytotoxicity can help make sense of potential side effects or safety concerns associated with medical therapies and products.

Let’s break it down simply and explore why this matters, especially in today’s world of advanced therapies and technologies.

What Is Cytotoxicity?

Cytotoxicity refers to the quality of being toxic to healthy cells¹⁻⁴. It means something—whether a drug, chemical, or particle—can damage or destroy living cells¹⁻⁴. In healthcare technologies, controlled-but-present cytotoxicity is often used to fight disease, such as chemotherapy drugs used to kill cancer cells. But unintended, uncontrolled, or prolonged cytotoxicity can cause harm to healthy cells and is something medical researchers and clinicians work hard to prevent.

There are two major contexts where cytotoxicity is critically important: ¹⁻²

1. The safety of medical materials, such as nanoparticles used for imaging, drug delivery, or diagnostics; and,
2. The immune system’s natural defence mechanisms, particularly the role of immune cells that kill infected or cancerous cells.

Nanoparticles and Cytotoxicity

Nanoparticles are extremely tiny particles (1–100 nanometers in size) that are being used more and more in medicine—for example, in targeted drug delivery and cancer imaging². Because these particles are so small, they can behave very differently inside the body compared to larger materials². Nanoparticles can enter the body either by accident (like through consumer products) or intentionally (like for medical treatment)². Before these materials are approved for medical use, researchers must rigorously test their effects on human cells to ensure they are safe.

Researchers use special lab tests to assess whether nanoparticles harm cells. Some examples include²:

• Cell staining methods: Dead or damaged cells absorb certain dyes differently than healthy cells.
• Measuring cell activity: Scientists check if the cell’s energy production or structure has been disrupted.
• Looking for stress signals: Harmful particles may cause oxidative stress or inflammation inside cells.

For example, carbon-based nanoparticles (like fullerenes and nanotubes) and metal nanoparticles (like gold or iron oxide) have all been tested to understand how their size, coating, and shape affect their potential toxicity².

The Immune System and Natural Cytotoxicity

The other fascinating side of cytotoxicity is how the body uses it to protect itself. One particular example if Natural Killer (NK) cells, which are specialized immune cells that kill infected or cancerous cells¹. Think of NK cells as the body's rapid-response SWAT team.

NK cells use two main tactics¹:

1. Releasing tiny toxic packages that punch holes in the bad cell and inject enzymes (called granzymes) to trigger the cell to self-destruct.
2. Switching on “death receptors” on the surface of dangerous cells, signalling them to undergo a controlled form of death called apoptosis.

This process is very targeted: NK cells are designed to avoid harming healthy cells¹. They have built-in safety mechanisms, including special proteins that block any accidental self-harm from their own weapons¹. Importantly, this natural cytotoxicity is a cornerstone of modern cancer immunotherapies¹. Some antibody-based treatments help guide NK cells to tumour cells, boosting this natural killing process¹.

Can Antiseptics Be Cytotoxic?

Not all antiseptics are cytotoxic, but yes, they can be and often are. Like many medical materials, some antiseptics can harm not only the intended bacteria but also healthy cells in the body³⁻⁴.

It’s commonly known that antiseptics are designed to kill or stop the growth of harmful microorganisms on skin, wounds, and surgical sites. However, in reality, the very properties that make antiseptics effective can also lead to unintended damage to healthy human tissue³⁻⁴. While cleansing wound sites to eliminate bacteria and other harmful pathogens is essential in preventing infection, excessive cytotoxicity can actually slow recovery despite the antimicrobial benefits³⁻⁴.

How Cytotoxicity Affects Antiseptic Use and Wound Healing

The ultimate goal of using an antiseptic is to prevent infection without harming the body’s natural healing process, and cytotoxicity can interfere with this balance³⁻⁴. When antiseptics damage fibroblasts and keratinocytes—cells vital for rebuilding skin and tissue—the healing process can be delayed or even disrupted³.

Types of Antiseptics and Their Cytotoxicity

Not all antiseptics are created equal³⁻⁴. Researchers have developed a helpful tool called the Biocompatibility Index (BI) to measure both how well an antiseptic kills bacteria and how harmful it is to human cells³. A BI greater than 1 means the antiseptic is more toxic to bacteria than to human cells³. Here’s what studies have found³⁻⁴:

• Chlorhexidine (CHX) products showed strong antibacterial action but also had a notable toxic effect on healthy cells, especially at higher concentrations.
• Povidone iodine products, often considered very safe, had lower cytotoxicity but also weaker antibacterial action in some tests.
• Silver-based antiseptics, like silver nitrate and silver sulfadiazine, showed strong cytotoxicity with little bacterial killing at early time points in lab tests, leading researchers to question their effectiveness in fast-acting wound care.
• Antibacterial soaps showed varying degrees of cytotoxicity and antibacterial effect, with chlorhexidine gluconate performing best in reducing bacteria in wound models, albeit with greater tissue toxicity.

Safety and Efficacy Without Compromise: The Role of Hypochlorous Acid in Non-Cytotoxic Wound Care Solutions

Hypochlorous acid (HOCl) is a substance that the human immune system naturally produces, specifically through neutrophils during immune responses, where it helps kill bacteria. Due to these antimicrobial properties, HOCl has been increasingly incorporated into wound irrigation solutions since World War I. More recently, these solutions have gained popularity in clinical wound care because they can effectively disinfect wounds while causing little-to-no harm to human cells (a mini-spectrum which depends heavily on the purity and stability of the solution). It’s an objectively remarkable quality in a medical solution.

In fact, a 2019 study⁵ investigated the antimicrobial effects and cytotoxicity (cell damage) of various commercial HOCl/NaClO wound irrigation solutions. The research showed that solutions with lower chlorine concentrations and near-neutral pH were significantly less harmful to human skin cells⁵. Some HOCl solutions showed no cytotoxicity to human keratinocytes (HaCaT) and skin fibroblasts (BJ) during 15 minutes of exposure, indicating excellent biocompatibility⁵. This balance between safety and efficacy is demonstrably crucial in wound care⁵. As a result, HOCl-based solutions with precisely controlled formulations offer a safer option for wound cleansing, particularly when protecting healing tissues is essential⁵.

Cytotoxicity: A Tool, A Risk, and A Balancing Act

The onus to understand cytotoxicity does not solely reside with researchers. For practicing health care professionals, it’s an increasingly critical part of making smart, safe daily choices in caring for their patients.

From the body’s natural immune responses to the way we cleanse and manage wounds, cytotoxicity plays a dual role: it can help fight infection, but it can also harm healing tissues if not carefully managed.

Advances like pure hypochlorous acid (HOCl) solutions starkly highlight how science is moving toward safer, more effective therapies. By continuing to study and respect the complex balance between killing harmful microbes and preserving healthy cells, we can improve outcomes for patients and move one step closer to optimal, evidence-based care.

For more information about Biomiq’s pure and stable hypochlorous acid (HOCl) based cleansing and irrigation solution for wounds, skin and burns, please read more about PureCleanse™.