You have a really weird idea of what hispanic blue collar workers’ lives are like. Some of them are from south of the border. Lots of them were born here. They buy food from supermarkets, live in low cost but hygenic housing, eat Mcdonald’s and do other American things like not get hookworm infections as children and not die from simple bacterial infections due to lack of penicillin. But there probably is something to the hygiene hypothesis. Which is why the white blue collar worker allergy to middle aged white woman allergy ratio is only 1:50. (The crotchety old white man to middle aged white woman ratio approaches infinity, as nearly as I can tell)
That said, people can certainly have multiple allergies. They can and do. It’s not really all that uncommon. Hypochondriacs and annoying, dramatic people just outnumber them somewhat.
The MSG thing cracks me up. “I have a documented MSG sensitivity!” Yeah, but doctors document a lot of dumb shit on a regular basis. Plenty of people waking around with bands that say Allergy: epinephrine. I suppose it’s possible that someone could have a sensitivity to an amino acid but why Chinese food? Would it be okay if the cook used some dashi broth instead of MSG out of a can? Japanese food cooking uses dashi and kombu in almost everything, that okay? How about sushi, wrapped in seaweed? Aged cheese? Probably one of the highest concentrations of glutamate of any food. Tomatoes? Between the wheat, tomatoes, and cheese a pizza contains more glutamate than a bowl of fried rice. I had a vegetarian lecture me about glutamate when she was would regularly eat seitan, which about a third glutamate by weight. Most fast food, but especially KFC, contains plenty of MSG. All of these are blown away by packaged food/soups (which have an unbelievable amount, multiple grams). But no one ever says, “I have a true medical MSG sensitivity. So I don’t eat cheese, KFC, or convenience food”. It’s always Chinese food of all things. It’s not like there wasn’t some interest in the topic at one time. Attempts at reproducing it were generally unsuccessful. It never got to the point where anyone could figure out a semi plausible mechanism. They just changed the name to hydrolized whatever protein and people shut the hell up about it.