In most cases occupational contact dermatitis is primarily caused by direct localised skin contact with chemical or physical agents, but its development may also depend on wider aspects of the occupational environment. Firstly, allergens may widely contaminate surfaces in sufficient quantity to elicit dermatitis; this is not as often true of irritants. Secondly, occupational contactants may enter the air as molecules, particles or droplets and elicit dermatitis. This can occur with irritants as well as allergens. Thirdly, low humidity of the air itself can cause dermatitis, as well as promoting the action of irritants and allergens on the skin. Specific examples are given of each of these wider environmental aspects and preventive methods are discussed.