Contact allergy from Frullania and respiratory allergy from Thuja.

Occupational allergic contact dermatitis in 52 forest-workers was caused by sesquiterpene lactones from liverworts (Frullania) and by usnic acid from lichens which grow on various trees including cedar (Thuja). Occupational asthma and rhinitis in 35 wood-workers was caused by wood dust of western red cedar (Thuja plicata). Characteristically, the respiratory symptoms occurred in the evening and at night and not during working hours; inhalation challenge with plicatic acid from the wood provoked immediate, late or dual (combined immediate and late) asthmatic reactions. Another class of compounds, tropolones, derived from Thuja plicata wood, was responsible for dermatitis in a wood-worker. These distinct industrial hazards in two groups of workers at the tree-felling and wood-working levels in the forest-products industry can be identified by clinical history and examination supplemented by specific cutaneous or respiratory clinical investigation.