The working environment itself causes occupational disease and injuries, fatigue, unsatisfactory man/machine relationships and physiological stresses. Risks are greater among the migrant workers who have no vocational training or industrial experience and whose illiteracy and ignorance make it difficult to understand written or oral instructions. Exposure to typical high temperatures or to high humidity causes heat stress. Special problems may also arise in connection with work at high altitudes or in thick forests.
A 1993 survey found that nearly 1 in 5 US workers had job-related back pain for a week or more during the previous year, and 22% had trouble with their hands (including carpal tunnel syndrome).