Occupational exposure to gas, dust, and fumes (GDF) increases the risk of asthma and eczema. We investigated the role of sensitization in the association between GDF and allergic conditions. A population-based sample of 788 adults from the West Sweden Asthma Study completed questionnaires and skin prick tests. After adjustment for confounders, GDF exposure was associated with a doubled risk of sensitization to mites, but not with other allergens. Mite sensitization also modified the effect of GDF on asthma. In mite-sensitized subjects, GDF was associated with physician-diagnosed asthma, adjusted OR 2.9 (1.2-7.2), and with wheeze, OR 2.4 (1.1-5.3). In non-mite-sensitized subjects, the corresponding ORs were 1.1 (0.5-2.6) and 0.6 (0.3-1.3). GDF was independently associated with eczema regardless of mite sensitization, but not with rhinitis. These novel findings suggest that components of GDF may act as adjuvants that facilitate sensitization to mites and that mite-sensitized individuals may be especially susceptible to inhalant occupational exposures.