I have a very nasty reaction to tobacco smoke. I might be allergic to it, but in any case, inhaling even a tiny bit is a DEEPLY unpleasant experience for me. Being around it nauseates me. And obviously it's not healthy for the person smoking it. Indeed, it's usually, eventually, lethal.
And yet, I have many friends who are, or have been, smokers. Most of them smoked socially. A few were chain smokers. Some did in fact blow smoke in my face on occasion. I survived. So did they.