The Department of Occupational Medicine at Aarhus University in Denmark has concluded that styrene may cause cancer in humans. Styrene is a colorless liquid that evaporates easily. In its pure form, styrene has a sweet smell. Manufactured styrene may contain aldehydes, which give it a sharp, unpleasant odor.
Styrene is widely used to make plastics and rubber. Consumer products containing styrene include:
- packaging materials
- insulation for electrical uses (i.e., wiring and appliances)
- insulation for homes and other buildings
- fiberglass, plastic pipes, automobile parts
- drinking cups and other “food-use” items
- carpet backing
These products mainly contain styrene linked together in long chains (polystyrene). However, most of these products also contain a small amount of unlinked styrene. 
The Danish survey was initiated by a 2011 poison scandal, where the Danish newspaper Berlingske Tidende gave voice to 20 former employees of the company LM Wind Power in Lunderskov near Kolding (formerly LM Glasfiber). All of the employees were seriously ill, allegedly due to interaction with styrene, which was used in windmill production. 
The study was published in the scientific journal Epidemiology. It covers 72,292 employees who worked for one of the 443 small and medium-sized companies in Denmark that have used styrene for the production of wind turbines or pleasure boats during the period 1968-2012.
The study concluded that occupational styrene exposure may be associated with Hodgkin lymphoma, myeloid leukemia, and cancer of nasal cavities and sinuses. 
“Via several national registers, we have identified the relevant companies and their employees, before coupling this information with the Danish Cancer Register. We have thus compared occurrences of different types of cancer in 72,000 employees, against the risk of these diseases in the general population who have not come into contact with styrene,” said Professor Henrik A. Kolstad
“It is important to know for present and former workers exposed to styrene that they are unlikely to have become ill by doing their job if they have developed cancer of the esophagus, pancreas, lungs, kidneys, bladder or a wide range of other types of cancer. This is also new and important knowledge in the USA, where styrene was added to the list of carcinogenic substances in 2011,” Kolstad said.
In the United States, the Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in the nation. These sites are then placed on the National Priorities List (NPL) and are targeted for long-term federal clean-up activities. Styrene has been found in at least 31 of the 1,689 current or former NPL sites. Although the total number of NPL sites evaluated for this substance is not known, the possibility exists that the number of sites at which styrene is found may increase in the future as more sites are evaluated. 
The EPA regards styrene as a “hazardous chemical”, especially in the case of eye contact, but also in the case of skin contact, of ingestion and of inhalation. Also, the agency described styrene to be “a suspected toxin to the gastrointestinal tract, kidney, and respiratory system, among others.”
In 2011, the U.S. National Toxicology Program described styrene as “reasonably anticipated to be a human carcinogen.” 
Kolstad emphasized that more investigation needs to be done to determine if styrene is the actual cause of the employee's disease. “It is a case of risk assessment: Should you use styrene, which might have serious — though unconfirmed — side effects in the form of cancer, or should you use epoxy products, which has less serious but well-documented side effects in the form of eczema?” he said.
Kolstad expects follow-up research results to be complete in spring 2017.