While it may sound bizarre, Dr. Levi A. Reiter, Professor of Audiology at Hofstra University in New York, has published several case studies establishing that a well-meaning kiss can actually permanently damage the hearing of the kiss recipient when the kiss is placed just outside the ear canal.
As explained in the article on the Healthy Hearing website linked to above, anatomically, the stapedial ligament connects the stapedial muscle to the stapes, one of three small bones within our middle ear that helps transmit sound to the inner ear. Dr. Reiter surmises that the suction of a kiss pulls the stapes away from the inner ear causing a tsunami of sorts in the inner ear fluids, and damaging the delicate outer hair cells permanently. Stapedial ligament damage also causes sensitivity to sound since this ligament is instrumental in protecting our inner ear from loud sounds. If the stapedial ligament is damaged, it can’t effectively perform its protective function, thus allowing too much sound to the inner ear, causing discomfort and sensitivity to sound.
Hearing loss due to kissing has now been labeled REKS, or Reiter's Ear Kiss Syndrome. Dr. Reiter stresses that it is important to publicize REKS to parents and caretakers of newborns since everyone loves to kiss babies. Since the ear canal of an infant is very small, the negative pressure applied to the ear canal during a kiss is going to have a much greater impact on the newborn's ear canal than on an adult ear canal. And since infants can't communicate hearing loss, any hearing loss resulting from a kiss could persist undetected for years until the affected child gets older. At that point, it won't be possible to trace the hearing loss back to a kiss, resulting in much unnecessary diagnotics.
The bottom line: keep kisses away from the ear.