The major part of the approximately 150 cm 2 surface in the human nasal cavity is covered by respiratory epithelium, across which systemic drug absorption can be achieved. The olfactory epithelium is situated in the upper posterior part and covers approximately 10 cm 2 of the human nasal cavity. The nerve cells of the olfactory epithelium project into the olfactory bulb of the brain, which provides a direct connection between the brain and the external environment. The transfer of drugs to the brain from the blood circulation is normally hindered by the blood–brain barrier (BBB), which is virtually impermeable to passive diffusion of all but small, lipophilic substances. However, if drug substances can be transferred along the olfactory nerve cells, they can bypass the BBB and enter the brain directly.,  
The most common side effects associated with fluticasone are headache , throat infection, nasal irritation, sneezing , cough , nausea , vomiting . Hypersensitivity reactions such as skin rash , itching , facial swelling, and anaphylaxis may occur. Some children may experience growth suppression when using fluticasone. A bloody nasal discharge ( nosebleed ) and septum perforation may occur. Fungal infection of the nose and throat, glaucoma , and cataracts are also associated with intranasal fluticasone.
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