I'm the same, if I swallow I get upset stomach or even stomach cramps, nausea. I remember reading about it, it's because of some specific protein that sperm contains, protein that cannot be digested as we don't have the enzyme to break it down. So pretty much the same thing as other proteins (dunno, milk, gluten?) intolerance.
Can you provide evidence for that as never heard of such?
Allergy to semen is a rare condition, thought to arise from some of the ingredients ... most likely the small protein content (although not sperm). It is a Type I allergy which means it is an immediate hypersensitivity reaction and will cause issues at the point of contact, be it vagina, oral cavity and skin. Whilst this could go on to cause Gastro Intestinal reactions if swallowed, it will not do this alone without an initial oral reaction.
There are some reports of semen causing stomach cramps not related to allergic reaction, but no obvious cause can be ascertained. This is extremely rare, although we appear to have two cases in this thread?
In terms of STIs the risk relates to the time the semen is in the oral cavity. Once swallowed and enters the stomach the STI risk should be eliminated.
If you are concerned about STI risk do not allow semen into your mouth at all. It can be argued that the risk potentially increases with time present in the mouth, so swallowing is likely to be the quickest way to reduce that risk. Swallowing certainly does not increase STI risk.
The real problem is that semen can be ‘unpleasant’ in consistency (although it is mostly water) and occasionally volume, which produces swallowing hesitancy. This can be a normal reaction to foods also.
Taste can be also be an issue of course, but taste will only take place whilst the semen is in the mouth, so swallowing is once again a quick way to get rid of the taste, although there is a natural reaction not to swallow something which tastes unpleasant but to spit it out instead. Think back to taking spoonful of childhood medicine and being told "swallow it and the taste will be gone"
Finally it goes without saying that of course you cannot get pregnant from swallowing …. or can you? Well only if you get into a knife fight afterwards.
External Link/Members OnlyRemarkable things those little spermatozoa