normal/healthy sinus, the air just comes right back out. In an inflamed
and partially obstructed sinus, you may force air in and that air may have
a hard time getting out, leaving a positive pressure in a given sinus.
This may be uncomfortable. Other explanations may exist, but this seems a
likely one in this case.
sense of smell with age, some more than others depending upon their
genetics. Some viruses can also damage the sense of smell. There are many
other ways that smell can be damaged, lost or attenuated. He would need to
see an Otolaryngologist for assessment.