Occupational rhinoconjunctivitis caused by the common indoor plant, Hoya compacta

Background: Allergic reactions to the common house plant Hoya compacta (HC) have not previously been described. Aims: To confirm HC as the cause of rhinoconjunctivitis in three horticultural workers. Methods: Greenhouse working conditions were reproduced in our challenge chamber. Results: All three cases developed rhinoconjunctivitis when working with HC plants. A control challenge was performed in two cases with iceberg lettuce causing no symptoms. Nasal volume measured by acoustic rhinometry (AR) fell after all three active challenges, but also after one of the control challenges. Conclusions: Our study confirms that HC may cause occupational rhinoconjunctivitis and asthma through a Type I hypersensitivity reaction. Specific inhalation challenges, nasal nitric oxide measurement and AR may be useful additional tools in supporting such diagnoses for occupational physicians to consider.