The scientific effort to describe the potential for styrene exposure to cause cancer in humans may be entering its last phase. Some scientists think it’s already over.

Enough already

The styrene toxicity database available today provides ample support for a conclusion of “no concern” for styrene and cancer.  To understand why this is a scientifically defensible position, we need to understand how scientists decide such matters.


Bad policy masquerading as science — Ignoring the weight of evidence, the National Toxicology Program listed styrene in the 12th Report on Carcinogens as a “reasonably anticipated” carcinogen.

Science uses precise methods to collect data, then uses these data to test hypotheses (theories). Scientific hypotheses need to be disconfirmable, meaning they are capable of being disproven empirically (using data). “The moon is made of cheese” is a disconfirmable hypothesis; it can be scientifically tested by collecting and weighing data. “My house will never be hit by a meteor” is not a disconfirmable hypothesis; its validity or truth cannot be tested using empirical evidence.

What scientists consider “true” are disconfirmable hypotheses that have a large weight of supporting empirical evidence.

Consider two styrene toxicity hypotheses. Either there is, or there is not, a significant potential for styrene to cause cancer in humans.  Can we find sufficient “weight” of scientific data supporting either of these theories?

For styrene, a very large body of scientific data can be used to test hypotheses about carcinogenicity.  Cumulatively, the evidence supporting the conclusion that there is not a significant potential for styrene to cause cancer is very heavy and the weight of the evidence in support of the alternative hypothesis is very light.

In summary, the large studies of composites industry workers tracked over several decades are free of any styrene-related cause of death, even though these workers were exposed to much higher levels than are common in workplaces today. Studies of workers in other industries, some of which suggest a possible cancer effect, had much lower styrene exposures, as well as the presence in the workplace of other chemicals known to be human carcinogens. Data from studies on DNA damage in styrene-exposed workers are weak, inconsistent and inconclusive.