I'm not sure whether you are referring to a cleanliness issue for women or men giving oral sex, or both. But we recently had a question over in ask_me_anything, regarding women's enthusiasm for giving bj's. Some women loved it, but many seemed to find it boring and/or somewhat uncomfortable to do for any length of time. There was only one woman who mentioned cleanliness as a factor. I completely concur with her, however. But then I'm a clean freak in general.