Unless you are ill, in which case you shouldn't be passing bodily fluids at all, there is really no reason why swallowing semen would put the partner in any danger. The semen is actually very useful for many things. The most obvious being the creation of a embryo. However, semen is also used as a facial pack in certain French spas. The semen acts as an astringent, tightening the skin. (I'm sure most guys have noticed that...)

And, then there are those females (and males, for that matter) who actually enjoy the taste. That means no grimace or supressed gagging sound.