Every time you hit the brakes, tiny particles of dust are released into the air. These particles, often invisible to the naked eye, come from the friction between brake pads and rotors. While much attention has been paid to the dangers of diesel exhaust, a new study reveals that brake dust — especially from copper-rich brake pads — may pose an even greater risk to our lungs.

The research shows that brake wear particles can disrupt the delicate balance of cells in the lungs, leading to inflammation, oxidative stress, and even changes in cellular metabolism. The main culprit is the emission of particles of copper, a metal commonly used in brake pads for its ability to conduct heat. The study concluded that brake dust from copper-enriched pads caused more damage to lung cells than diesel exhaust particles.

“We’ve known for a long time that air pollution is bad for our health, but we’re just beginning to understand how different sources of pollution affect us in different ways,” said James G. H. Parkin, the lead author of the study.

The Invisible Threat

Air pollution is a global health crisis, responsible for millions of premature deaths each year. Fine particulate matter, known as PM2.5, is especially dangerous because these tiny particles can penetrate deep into the lungs and even enter the bloodstream. While much of the attention has been on exhaust from vehicles, non-exhaust sources like brake wear, tire wear, and road dust are coming increasingly into focus.

Brake wear alone can account for up to 55% of non-exhaust particulate emissions. And as the world shifts toward electric vehicles, which are heavier and produce more brake dust, this problem is only expected to grow. “We need to think about the whole picture when it comes to air pollution,” the researchers wrote.

The study from the University of Southampton in the UK compared brake dust from four types of brake pads: low-metallic, semi-metallic, non-asbestos organic (NAO), and ceramic. The researchers exposed lung cells to these particles and found that dust from NAO and ceramic pads, which contain higher levels of copper, caused the most damage. These particles trigger oxidative stress, inflammation, and even changes in how cells produce energy.

Copper: A Double-Edged Sword

Copper has long been used in brake pads because it helps dissipate heat, preventing brakes from overheating. But this study suggests that the same copper that is so useful in brakes becomes dangerous when inhaled. The researchers found that copper in brake dust accumulates in lung cells, disrupting their normal function.

Copper is essential for life, but too much of it can be toxic. When these particles enter the lungs, they release copper ions, which can overwhelm the cells’ natural defenses. The study showed that when lung cells were exposed to copper-rich brake dust, they produced more reactive oxygen species — molecules that can damage DNA, proteins, and cell membranes.

The researchers also found that copper-rich brake dust activated a pathway known as pseudohypoxic signaling, which is linked to diseases like cancer and pulmonary fibrosis. This pathway is usually activated when cells are deprived of oxygen. But in this case, it’s being triggered by oxidative stress caused by copper.

To confirm that copper was the driving force behind these effects, the researchers used a copper-selective chelator — a compound that binds to copper and prevents it from interacting with cells. When the chelator was added, the harmful effects of the brake dust were significantly reduced. This tells us that copper is the main factor in driving the toxicity of brake dust.

What Does This Mean for Public Health?

The findings raise important questions about how we regulate air pollution. Currently, most regulations focus on the mass of particulate matter, without considering its composition. But this study suggests that the specific chemicals in particulate matter — like copper — can have a big impact on health.

Reducing the amount of copper in brake pads could be a simple way to make brake dust less harmful. Some U.S. states, like California and Washington, have already taken steps in this direction — though their primary goal was to protect waterways from copper runoff, not to safeguard lung health.

“New brake pad formulations could reduce overall dust emissions or be designed to exclude toxic components,” the researchers suggested. They drew a parallel to the past removal of asbestos from brake pads, which was once a common but hazardous material.

For now, individuals can take steps to minimize their exposure, such as using high-quality, low-metal brake pads and avoiding prolonged time in heavy traffic. But the real solution lies in targeted legislation and innovation.

In the meantime, the researchers hope their findings will encourage policymakers to take a closer look at the hidden dangers of brake dust. This study is a reminder that we need to consider all the sources of pollution, not just the ones we can see.

The findings appeared in the journal BMC.