As cars age, certain wear and tear is to be expected. One of the realities of frequent driving, particularly for drivers who routinely drive in stop-and-go traffic, is the gradual deterioration of brake pads. Do-it-yourselfers can replace brake pads on their own, but those that do should be aware of a potential hazard when doing so.
The Mesothelioma Center says that brakes sometimes contain asbestos due to that material’s heat-resistant qualities. As brakes start to wear down over time, the asbestos can escape. The Occupational Safety and Health Administration (OSHA) says that, while many new automotive components are asbestos-free, asbestos hasn’t been eliminated entirely from the industry. That is why mechanics and do-it-yourselfers need to exercise caution when repairing or replacing brakes. 
Brake dust may inadvertently expose individuals to cancer-causing asbestos through inhalation or ingestion. OSHA says that exposure to asbestos, if not properly controlled, can cause mesothelioma, lung cancer and asbestosis. Symptoms may not appear for years or even decades after contact with asbestos fibers.
The Mesothelioma Center estimates that asbestos is present in 30 to 80 percent of brakes and other components. The routine task of “blowing out” brake surfaces, which involves using an air hose to clean the surfaces of brakes and rotors, is one of the most common ways people are exposed to asbestos through brake dust.
Gray-black brake dust is made up of iron particles formed by the grinding of the brake rotor by the brake pads. However, brake dust also can contain some metallic elements and other components housed in the brake pad — including asbestos. 
The automotive resource YourMechanic says that, while brake dust is not indicative of a poor braking system, over time brake dust can corrode the clear coat on a car and may eat into the aluminum alloy surface of the wheel. That is why so many drivers try to clean away brake dust, potentially exposing them to dangerous materials. 
DIYers may be better off visiting professional service centers to have brakes addressed rather than doing the job on their own. OSHA says all automotive brake and clutch repair facilities in the United States must comply with the OSHA asbestos standard. These include using negative pressure enclosure/HEPA vacuum systems and low pressure/wet cleaning methods. 
While asbestos is being phased out of many automotive components, it is always best to treat bakes, clutches and more with extra caution in the event that asbestos is present.