Not all allergic reactions are visible. In fact the worst and most dangerous of my allergic reactions are *not* visible, because they involve the inside of my throat and mouth, my lungs, and my brain. You can’t see any of those things, but I will stop breathing all the same.
Many folks I know who have life-threatening allergic reactions experience only neurological or gastrointestinal symptoms which are in fact incredibly dangerous if allowed to continue, but not in any way visible. Getting people to understand what they go through and believe that the precautions they take are necessary and not just paranoid or attention-seeking is incredibly difficult in that kind of situation. Even well-meaning and otherwise reasonable loved ones will often conclude hypochondria, except that it *isn’t* hypochondria if you are actually sick!
Once upon a time, three years ago now, I had a severe and visible allergic reaction to the tiniest trace of corn derivative. It actually didn’t turn out to be that dangerous (never progressed into any internal issues), but it *could* have. At the time I took pictures because I thought it was weird and actually kind of hilarious in a sick way, but it turned out to be a very good way to get people to understand that yes, this allergy is real, and yes, it is possible to be *that* sensitive.
If you or a loved one are an allergy sufferer, and have a visible reaction, I highly encourage you to document. Obviously do what you need to do to assure your safety first, but get pictures if you possibly can. It may come in handy later.