I've only been to Vietnam and Hong Kong and only on vacation so I didn't see that much. I don't think it is anything you won't be able to handle but it will be different than the US. In Hanoi in the old part of town it smelled like sewage and garbage in a lot of places. There was a lot of trash on the ground but it did seem like people were cleaning it up all the time. I think it is just what happens when there are a ton of people living very closely with very old infrastructure. Hong Kong was much more modern and cleaner but it had urban smells like dumpsters and urine. It wasn't any dirtier than any other urban area I've been in though, for example downtown New Orleans and Chicago are just as bad if not worse.
The air quality seemed good enough in both.
In Vietnam you will see things like bloody meat being sold from a piece of cardboard on the sidewalk. It's not up to modern food safety standards. Having to see it isn't that bad and probably something good to be exposed to. I definitely didn't buy any of it though.