Worker Health Study Summaries – Stilbene Manufacturers

Research on long-term exposure

Stilbene Manufacturers (4,4′-diaminostibene-2,2′-disulfic acid (DAS))


Study Background

The exposed group included 30 men who made DAS in 1991 and 20 men who made DAS in 1981-1983. They were compared to 35 men who worked in Additives and were mainly unexposed to DAS. Most of the information in the study comes from hourly workers.

We compared the DAS workers to the Additives workers to see if there was a difference between them. A difference might suggest that making DAS might have affected DAS workers.

Study Results


Testosterone is an important “male” hormone. It causes the sexual changes in men at puberty. Sexual performance can be affected if a man does not have enough testosterone.

No man in the study had testosterone levels lower than normal.

However, even though most men’s testosterone levels were normal, we did find an effect. On average, the men exposed to DAS tended to have lower testosterone levels than unexposed men. This was true in both the 1991 DAS workers and the 1981-1983 DAS workers.

The longer men had made DAS, the lower their testosterone levels tended to be. This would suggest that DAS or something else in the DAS area may be affecting testosterone levels.

Sex Life

We asked the men in the study to answer some questions about their sex life. The purpose was to see if men exposed to DAS reported symptoms of sexual problems more often.

DAS workers reported a lower interest in sex more often than comparison men who worked in Additives. The DAS workers also reported having problems with erections and ejaculation more often.

Unlike Additives workers, DAS workers reported an improvement in their sex lives when they had been away from work for a day or more. This might suggest that something at work may be affecting the sex lives of DAS workers.

Other Effects

More 1981-1983 DAS workers had other effects such as small testicles, enlarged breasts, or lower levels of another hormone called FSH. These occurred in very few workers, so it is hard to know if they were connected to chemicals at work.

We did not see any sign that DAS workers had more trouble fathering children than unexposed workers. However, we would need a study with more workers to tell this for sure. Similarly, there weren’t enough men in the study to look at possible effects on children (such as birth defects, miscarriages, or premature babies.)

What Caused the Effects Seen?

We don’t know for sure what caused the effects seen. DAS is chemically similar to one of the “female” hormones or estrogens. This could explain the effects seen. Studies have shown that other chemicals similar to estrogen hormones have caused these types of effects, often to a greater degree.


The process changes that took place after 1983 probably reduced workers’ exposure to chemicals in the DAS area. The new process is more enclosed and does not use the anti-foaming agent 2-ethyl-1-hexanol (2EH). Even current workers, however, still have the potential for exposure.

We weren’t able to tell which chemicals in the DAS area may be linked to the effects seen. In addition to DAS itself, animal studies have linked two other chemicals to possible reproductive problems in males.

The first is 2EH, which was used in the old process to prevent boiling over. The second is PNT, which is still used as the starting material for DAS.

Is the Current DAS Process Safe?

We would have liked to be able to answer the question of whether the current process is safe. However, since only a few DAS workers have worked with just the new process, we cannot answer this question.


We recommend that the following steps be taken to reduce exposure to chemicals in the DAS process to the lowest possible level:

  • Always wear gloves in the DAS processing areas. Avoid skin contact with chemicals.
  • Wash your hands before eating or drinking at work.
  • Keep surfaces clean of the yellow material that builds up.
  • Keep the DAS process areas clean, especially the final bagging and filtration areas.
  • Shower daily at the end of your shift.
  • Change into clean clothes and shoes before leaving work.

Talk to your doctor if you have any problems related to sex or other health problems.

Any Questions?

If you have any additional questions, please feel free to call NIOSH at 800-356-4674.


Whelan E, Grajewski B, Wild D et al. (1996). Evaluation of Reproductive Function Among Men Occupationally Exposed to a Stilbene Derivative: II. Perceived Libido and Potency. American Journal of Industrial Medicine 29:59-65.

Page last reviewed: April 8, 2020