Consider the aversion to large crowds

Enochlophobia refers to the fear of crowds. Not everyone who feels uncomfortable in a crowd lives with enochlophobia. Rather, this phobia involves irrational thoughts and behaviors that are excessive in relation to the actual danger in a situation.

Says the web.

Now, how much of that aversion is an early immune reaction? In a crowd, there is dangerous viruses and there are early immune responses. Evolution may have inserted a biological basis for crowd aversion. Immune reactions and anxiety can be confused and they are related.  Human centric bacteria, in large doses could easily cause a flush reaction, make us sweaty, uncomfortable around crowds.