I think it's also people who are just prone to being too sensitive to content that's not 90% "wholesome". Whether it be scary things, violence, vulgarity, or even the mildest of sexual references, they just have an severe and instant aversion and sensitivity to it.

I find a good majority of people who develop such issues turn out to to be women. Though ironically, there's a lot of women who have the opposite response and have an almost grotesque level of interest in horror.