I've heard that too, but I'm somewhat skeptical about it. The fact that most DL vapers are satisfied with such low nic levels is what makes me question it.
The size of the particles or droplets carrying the nicotine perhaps, but certainly not the nicotine molecules themselves. Molecules areTheory is the nicotine molecule in vapor is larger than the nicotine molecule in smoke, so the vapor molecule may not get into the lung's tiny alveoli (air sacs) for absorbtion.
I'll vouch for that. I've often described myself as "an MTl vaper, with the 'l' being lower-case for a reason."So in theory, its not necessary to inhale vapor into your lungs to absorb your nicotine.
Of course inhaling into the lungs isn't required for tobacco smoke either, with cigar and pipe smokers traditionally inhaling little, if any.
FWIW, exhaling through my nose doesn't cause me any problems.