Polyps 1... In some cases, polyps grow into the nasal passage. They usually originate at the sinus openings. Polyps are like teardrop-shaped collections of inflammatory cells, fluid, and tissue. They are covered by a mucous membrane. They can grow in response to infection, allergy, locations of abnormal contact, or for unknown reasons. When polyps are widespread, it is usually from some underlying mucosal abnormality. 1999 Peter Casano, M.D.