I was worried about this in nursing school (in addition to vomit which REALLY gets me). One of my clinical instructors suggested wearing a mask (if it's the smell that gets you). A friend of mine was recently going through a CNA program, and they point blank told her NOT to wear one because it's insulting to the patients. I asked my instructor about that, and she asked back: Well, isn't it more insulting if you gag or vomit on your patient? I figured, yup...
Other than that, you get used to it. Just sticking a foley in or cleaning a penis or vagina. It's something you'd never think of as "normal," but it truly becomes just that!
I'm convinced we become desensitized to certain sights and smells too...
Oh, and if the smell just overwhelms you, bring some menthol scent with you. My unit keeps it. If someone smells bad, they'll pour a little of the liquid on some gauze in a medicine cup and tape it on/outside of their door or set it on the nurse's desk. See if you can get away with that...
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