Flonase warnings. You may not experience the full benefits of Flonase for two weeks or more after starting treatment. Fluticasone may also make it harder for your body to fight off infections. While taking the drug, your body may be less able to manage the stress of surgery, illness, severe asthma attack, or injury. While taking fluticasone, you should avoid people who are sick, especially those with chickenpox or measles. If you get one of these infections or if you develop related symptoms, call your doctor right away.