I read somewhere that its not recommended to bike on roads busy with cars because the pores in lungs open up while biking and all that polution goes straight in

I read somewhere that its not recommended to bike on roads busy with cars because the pores in lungs open up while biking and all that polution goes straight in. I noticed some people are biking on dirt trails parallel to the paved trail because the paved one is too crowded with people, their children and childrens strollers and all that.