The incidence of non-Hodgkin lymphoma (NHL) has increased markedly over the past four decades in most countries.¹ The HIV epidemic contributed to this increase, beginning in the 1980s, but the remainder is largely unexplained. The remaining increase does not appear to be due to diagnostic changes and it cannot be strictly due to genetic factors because gene frequencies do not change rapidly enough to cause such large changes in rates over such a short period of time. We must, therefore, look to changes in the level and/or distribution of environmental factors to explain these rate increases. Possible environmental risk factors include occupational and environmental chemicals, microbes, diet, physical inactivity, and other lifestyle factors.

Although occupational exposures may contribute to the development of NHL, they are unlikely to explain the worldwide rise in incidence because the increase occurs among men and women and in developed and developing countries. No group of occupational exposures is likely to affect all of these populations. More widely spread exposures among the general population, such as viruses, diet, lifestyle activities, and general environmental chemicals, are more likely candidates.

Nonetheless, although occupational exposures may affect a smaller …