It's extremely well known that exercise is one of the best thing you can do for your immune system. It even assists in making the proteins that repair DNA... which is at the basis of your overall health.
There's also a shit load of consumption strategies that assist your immune system & make that "explosion" you speak of less likely.
"perfectly normal" people exploding when they meet? I think you mean "seemingly" perfectly normal. If one person's coody'z causes the other person to become violently ill then there would be a pre-existing condition in one or both of them that has gone un-detected. Some kind of allergy maybe... but even a lot of allergies can go away in an optimized immune system.
I'm open though... if you can share how 2 perfectly healthy people with optimized immune systems explode when they meet just through some weird chemistry... go ahead & dazzle me with some links & I'll take a look.