This is just a simple example of how bathing/changing clothes can affect your health. In the middle ages, you would have been walking in pathogen soup in all those dirty, sweat/urine/etc laden clothes you couldn't change out of.
Don't discount the impact of simple cleanliness. Pristine countryside? Doesn't exist. Go travel to one of those beautiful vistas you see in paintings, untouched by humanity and drink the clear stream water. Then spend the next few days doubled over in pain from all the parasites that live in the water, having arrived there from animal feces.
Nah, in the middle ages you'll be drinking whatever water is in your village's stream or watering hole, and you'll be glad for it too, after you carry it half a mile on your back to your house. If that water gets contaminated with cholera, you'll blame the sickness on the wrath of an angry god, or perhaps a jealous neighbor who witched you.
> Bathing [...] is not that important for health.
What???
Are you serious? You don't think living in a tiny room with 10 family members and all kinds of animals (along with all of the lice, fleas, diseases, etc. that go along), with a wood fire filling the whole place with eye-stinging, lung-choking smoke, was a "toxic environment"? You'd be eating mostly grains, with very occasionally some meat, and if it spoiled you'd still figure out some way to eat it, because otherwise you'd be going hungry altogether (and that would happen anyway, in poor harvest years). The water would be whatever you had nearby, probably infected with all kinds of pathogens from the excrement that would inevitably wind up there. You'd maybe have a sweat bath or sponge bath once every week or two if you were lucky, using the same water for the whole family. You certainly wouldn't have more than a few changes of clothes, which you'd wear for days or weeks at a time.
I suggest you spend some time with rural peasants in a developing country before arguing about toxic environments or nutrient-deprived food.