i thought retrohale was exhaling the smoke through nose. french is inhaling smoke through nose
Retrohale is when you take in a puff and push it out through your nose via your upper air passages thereby bypassing your lower respiratory system that leads to your lungs, etc. French inhaling is when you take the same puff but immediately blow it back out your mouth in such a way that as the smoke travels upward, you breath in through your nose thereby taking in some of the smoke you just blew out; this process does lead to some smoke going into your upper lung area. That said, with regard to how much smoke is touching respiratory membranes in general, retrohaling is far worse as the entire puff touches part of the lining of your upper airways, while with french inhaling, in general, only a small portion get ingested (unless, that is, you really focus your efforts on taking in as much as the puff as possible like people who vape do, but with pipe smokers, we generally just want to take in enough to taste the aroma so to speak, so it's very little of the puff that gets inhaled through the nose). Some may argue that the former is better for you because the smoke doesn't go into the lungs, I would argue that it depends where you live. If you live in a big city and/or a city with a lot of pollution, you probably don't want more chemicals going into your lungs so if that was a concern to you, you should probably retrohale, but if you live in an area like I do which has very clean air, I would much rather come into less contact with the smoke overall by french inhaling (regardless of whether it goes into the lungs) than more by retrohaling; plus, to me, I get a more complete flavor profile than I do by retrohale. But that's just my take on it, everyone has their own opinion of course.