Nasal polyps, as you are probably well aware, are really an overgrowth of the normal lining within the sinonasal tract (called mucosa). Most otolaryngologists
(ENT aka Ears Nose Throat physician) agree that the theory why they form revolves around chronic inflammation. In an inflammatory state, tissues swell, and if they are inflamed for long enough, they can every hypertrophy (or grow). In the case of nasal polyps it is assumed that the mucosal lining is inflamed and swollen for long enough to cause hypertrophy, and eventually enough overgrowth to form polyps. Polyps then cause a mechanical obstruction within the nose that can (and usually does) obstruct the outflow of mucous from the sinuses which can lead to infections (which cause more inflammation, and so the cycle continues). Surgery
removes the obstruction (i.e. polyps) and allows topical medications (which have become a very common treatment post-operatively in chronic sinusitis and sinonasal polyposis) to decrease inflammation. Surgery however does not fix the root cause of whatever was causing the initial inflammatory response in the mucosa that led to the formation of polyps. In many cases allergies play a role, but there is a lot of research into the actual causes of sinonasal polyposis. What we do know is that this tends to be a chronic problem, and it is not uncommon to need revision surgery in the future due to polyp re-growth. Typically we choose to operate on sinonasal polyps once all medical options have failed. I hope that this is helpful, and I would recommend making an appointment to discuss it with your ENT.