It is theoretically possible to become desensitized to any stimulus if it is encountered enough. However, I feel there may be a high degree of psychology involved in this equation as well. In other words, it is probably inadequately explained by neurobiology alone but depends on the environment, perhaps even more than it does on biology. It would not be outside the realm of possibility to consider that someone may be more sensitive in familiar surroundings with well known people as opposed to a strange or new situation with people who are unknown.
HappyD