In summary, while wearing a face mask might offer minimal benefits in terms of retaining some moisture around your nasal passages due to breath capture and reduced airflow exposure to dry cabin air, it does not effectively keep them moist during high altitude flights. The primary concern remains that airplane cabins are inherently dry environments that can lead to discomfort regardless of whether one wears a mask.

Thus, wearing a face mask will not effectively keep your nasal passages moist during a high altitude flight.