The foundation of modern materials, the strength and special properties of carbon nanotubes are all valued. But concerns about how harmful it can be when inhaling the lungs are surfaced. As more of these materials are produced globally, scientists are competing to figure out how they affect human health. Pay special attention to how their shape and stiffness affect the risk of lung disease, including cancer.
A research team led by Professor Hiroyuki Tsuda of the University of Nagoya City has carefully studied the stiff and flexible versions of these tubules. Their study, published in the journal Nanomaterials, reviews a series of early animal experiments that explore how these materials interact with lung tissue. Their comments provide new evidence that challenges past decisions about how risky these materials are to health. The team noted: “MWCNT-7 acts similar to long fibers that are non-nanoparticles and induces mesothelial carcinogenesis.”
Previously, the International Health Organization IARC listed a carbon nanotube called Mitsui multi-walled carbon nanotube 7, which may be harmful to humans, but there is not enough information to determine the impact of other types of carbon nanotubes on human health. Multi-walled carbon nanotubes are tiny cylindrical fibers made of carbon atomic layers, while carbon nanotubes with more layers exhibit higher stiffness. Therefore, their length and stiffness suggest that they may be carcinogenic, similar to longer rigid asbestos fibers, well-known human carcinogens. This also suggests that thinner flexible carbon nanotubes may not be carcinogenic. However, newer long-term studies using indoctrination into rat lungs have shown that both stiffness and flexibility types lead to lung cancer. This challenges early studies, which are short-term or injections into the peritoneal cavity. It is worth noting that even small exposure to stiffness types leads to the development of mesothelioma, the occurrence of mesothelioma, a serious cancer that affects the inner lining of the pleural cavity. While bendable types may seem less dangerous, they can also cause damage over time if inhaled regularly.
Perhaps the most important point is that, as shown in the figure, the shape and physical composition of these particles have different effects in the pleural cavity and lungs. Harder and thicker nanotubes are more likely to pierce and damage cells and cause tissue damage and inflammation, such as asbestos. Mitsui multi-walled carbon nanotube numbered 7, consisting of multiple concentric tubes, which act like non-nanoparticle long fibers and trigger the cancer-induced activity in the mesothelial. This highlights how the shape of the nanotubes plays an important role in danger in the pleural cavity. As Professor Tsuda explains, “Rigid MWCNTs are not easily engulfed, retained in the chest cavity and induce chronic inflammation and genotoxicity.” In contrast, inflammation in the lungs is associated with activation of macrophages and activation of inflammatory cytokines as well as thicker, harder carbon nanotubes and thinner, thinner, flexible carbon nanotubes all interact with macrophages in the lungs and induce inflammation and tissue damage. If carbon nanotubes are not removed from the lungs, it can cause cycles of inflammation and tissue damage, which can lead to cancer.
The researchers examined several studies in which carbon nanotubes were attracted by injection, instillation or respiration. Injection means using a syringe to deliver material directly into the body and mimicking inhalation in the air. Although injection tests help identify basic dangers, it is the long-term breathing and drip exposure studies that reveal the strongest link to cancer under more realistic working conditions. In these tests, animals instilled with stiff nanotubes instill tumors in the lungs, supporting concerns about long-term respiratory injury.
In a broader context, scientists have called on health officials to re-study the current assessment of carbon nanotube toxicity. Reassessment refers to careful reassessment of existing health classifications. They concluded that the current findings support the reevaluation of cancer classification of multi-walled carbon nanotubes. They believe that all forms (whether thick or thin) should be judged by the performance of long-term exposure to long-term exposure, not just older short-term tests. This change is especially important for industries that use these materials, which help protect workers and shape better safety policies. Professor Tsuda stressed: “These results support the reassessment of the oncogenic classification of MWCNT.”
In commercial products, the wider use of multi-walled carbon nanotubes has kept the study on time and alert. Commercial products refer to goods sold on the market. The news is clear: With the advent of new technologies, their health risks must be carefully evaluated. This study encourages a shift in the way materials are judged, not just through their making, but also through how they behave when used in the real world.
It is important that industry, researchers and governments work together. Identifying toxic materials is the first step in ensuring safe production and use of the material. Importantly, the fact that the material is toxic does not mean that it should be prohibited, but measures should be taken to ensure safe manufacturing and use of the material. To make another analogy with asbestos, it was at a time when human death was associated with asbestos that companies in many countries had become overdosed. In contrast, the production and use of many other toxic compounds conventionally is conventional. For example, formaldehyde is a well-known toxin that is also carcinogenic in humans. However, government safety regulations allow it to be widely used in industries, consumer products, research and medicine. Similarly, we believe that safety regulations regarding the manufacturing and use of carbon nanotubes can also safely use these extremely valuable materials. However, the first step in implementing these safety regulations is to identify toxic/carcinogenic materials. The researchers concluded that the data they proposed suggest that the carcinogenicity of carbon nanotubes should be reassessed, and they suggested that once carcinogenic carbon nanotubes are identified, safety regulations can be formulated to appropriate goals, with the aim of allowing the safe manufacturing and use of these very valuable materials.
Journal Reference
Ahmed Ohm, Naiki-Ito A., Takahashi S., Alexander WT, Alexander DB, TsudaH. Nanomaterials, 2025; 15 (168). doi:
About the author
Omnia Hosny Mohamed AhmedBorn in Aswan, Egypt in 1989, he is a clinical toxicologist and researcher. She earned her 2012 PhD from Sohag University and completed her master’s degree in Clinical Toxicology at Aswan University in 2019. Currently, she is a lecturer in the Department of Forensic Medicine and Clinical Toxicology at Aswan University. Ahmed is also affiliated with the Nanotoxicology Project Laboratory at Nagoya City University in Japan, where she contributes to the research on lung toxicity and carcinogenicity of nanomaterials, including the carbon nanohorns and carbon nanonuo blues. Her research has been conducted at international conferences such as the Japanese Society of Toxicology. As a student of the Japanese Toxicology Society, Ahmed actively engages in the field of toxicology through academic and collaborative research.
Dr. Aya Naiki-Ito He is a doctor and researcher specializing in experimental pathology and tumor biology. She holds both a MD and a Ph.D. Degree, affiliated to Nagakoshi University in Japan. Her research focuses on mechanisms of carcinogenicity, especially related to nanomaterials and environmental toxins. Naiki-Ito contributed to the study of the toxicological effects of various substances, including carbon nanotubes, on the organ system. Her work often involves the development of novel animal models to study disease progression and potential therapeutic interventions. Through her research, she aims to enhance understanding of cancer development and contribute to the development of effective prevention and treatment strategies.
Professor Hiroyuki Tsuda He is a leading expert in the fields of nanotoxicology and cancer, and is currently leading the Nanotoxicology Project Laboratory at the University of Nagoya, Japan. With a PhD from Tokyo Institute of Technology, Tsuda is committed to studying the health effects of nanomaterials, especially carbon nanotubes. His research greatly contributes to understanding the lung toxicity and carcinogenic potential of these materials. Tsuda’s work includes long-term in vivo studies that evaluate the effects of nanomaterials on lung and pleural tissues, thus providing important insights into their safety. He also participated in the development of international guidelines for training toxicology pathologists, emphasizing the importance of strict scientific standards in non-clinical toxicity research.
