Recently we reported that asbestos fibers were found in Chinese-made crayons and powder from children’s crime scene fingerprint kits that were found at stores in the San Francisco Bay Area — but why is that such a concern?

A study published Wednesday by an environmental health advocacy organization found that the substance was present in 28 boxes of crayons and two of 21 fingerprinting kits that were purchased both online and at physical stores in the East Bay area, according to an SFGate report.

There weren’t large amounts of asbestos present, but the problem is there is no such thing as a safe amount of exposure to asbestos.

Why? Asbestos is a naturally occurring silicate mineral which consist of thin, fibrous crystals. Each visible fiber has millions of microscope “fibrils” that are released via a number of processes.

It’s been 4,000 years since we first began to mine asbestos, but it didn’t happen on a large scale until the 19th century as manufacturers and builders began to see the advantage of using asbestos, not realizing their danger. They are resistant to fire, heat, and electrical and chemical damage, and they are cheap. Therefore, builders used it in electrical insulation for wiring as well as building insulation.

But in modern times, we’ve learned that prolonged exposure to asbestos and the inhalation of their fibers can cause fatal illnesses including lung cancer, mesothelioma, and asbestosis. Concerns about the substance first arose in the beginning of the 20th century, which it becoming heightened in the 1920s and 1930s. By the 1980s to the 1990s, asbestos had basically been banned outright in most developed countries.

Asbestos cases can emerge decades after the end of exposures, and asbestos litigation as become the most expensive mass tort in U.S. history.