Objectives The purpose was to examine if stainless steel and mild steel welding confers an increased risk of bronchial asthma.

Methods A Danish national company-based historical cohort of 5,499 ever-welders and 1,514 never-welders was with the Danish Medicinal Product Registry followed from 1995 through 2011 to identify the first-time redemption of asthma pharmaceuticals including Beta-2-adrenoreceptor agonists, Adrenergic and other drugs for obstructive airway diseases, Inhaled Glucocorticoids. Lifetime exposure to welding fume particulates was estimated by combining questionnaire data on welding work with a welding exposure matrix based on more than 1000 personal measurements of ambient air concentrations of welding fume particulates. The estimated exposure accounted for calendar-time, welding intermittence, type of steel, welding methods, local exhaustion and welding in confined spaces. Hazard ratios (HR) with 95% confidence intervals (CI) were calculated using a Cox proportional hazards model adjusting for potential confounders.

Results The average incidence of redemption of asthma pharmaceuticals in the cohort was 17/1000 years (95% CI 0.01–0.02). Asthma pharmaceuticals were not redeemed more often among stainless steel (n = 3874) and mild steel welders (n = 1625) than among never-welders. Among ever-welders redemption of asthma pharmaceuticals was not related to life-long exposure to welding fume. Analyses of specific subgroups of asthma pharmaceuticals did not reveal consistent associations with welding exposure. However, among non-smoking stainless steel welders the risk increased with cumulative welding dust exposure (HR for high- vs. low level exposed 1.41, 95% CI 1.06–1.89).

Conclusions The results showed no consistent association between lifetime exposure to welding fume and use of asthma pharmaceuticals. However, an increased risk of asthma pharmaceuticals among non-smoking stainless welders may indicate that stainless welding does confer an increased risk of asthma, which escapes detection among smokers having a high prevalence of obstructive airway disease.