Fluconazole is an antifungal medication that works well for treating asthma caused by fungal infections, but may actually worsen asthma from other causes. In mice with allergic asthma, fluconazole killed beneficial bacteria and promoted the growth of harmful bacteria that increased inflammation. This study suggests that fluconazole should only be used for fungal-related asthma and careful monitoring is needed if used in patients with regular asthma.