[shvcko99]

I know that most plastic bags are made of Polyethylene which should be inert, in that case, is it fine to repeatedly use them forever? Could it attract germs, bacteria, virus or other chemicals in the air and stay in the bags for long time?
I hope this is not an odd question because of protecting the environment I like to reuse plastic bags but sometimes I am worried about putting raw food without packaging e.g. vegetables, meats into well-used plastic bags.

[Borek]

You can always wash the bag (env question: is washing ecologically cheaper than the bag itself?). In general they are not much different from any other thing used in a kitchen.

[Enthalpy]

Small parts of food etc will break away and stay in the bag where they rot. So hygiene applies here too.

Polypropylene and polyethylene usually don't participate in such processes, so they would be favourable.

Reuse forever, no: sunlight destroys most polymers sooner or later. Atmospheric ozone too.