You can have an allergy to smoke. Or merely an intolerance. Or asthma. Either way, it causes an involuntary physical response. If someone smokes near me, I will start coughing. And when I'm coughing, I can't exactly move easily. I've coughed hard enough to throw up from an asthma attack before. I generally try to be observant and give smokers a wide berth, but it's happened before that I was in a crowd downtown, and a guy turned around and exhaled a lungful of cigarette smoke right as I was breathing in. I was coughing and choking so hard my eyes were watering. Thankfully? My friend was with me and dug my inhaler out of my bag for me. It's not just cigarette smoke, either. I can't stand incense. I can't even stand too close to a campfire. Or a barbecue. Or be downtown on a smoggy day. If someone did that to my great-aunt (she has emphysema, only 15% lung function, and is on oxygen), she could die. She doesn't get out so much anymore, but people sometimes don't THINK. If you have a habit that inconveniences other people, the onus is on YOU to make sure that you don't inconvenience people more than you have to.

Exactly. As I've said before: smokers can choose to stop smoking; I can't choose to stop breathing. And my allergic reactions to tobacco smoke are life-threatening if not treated immediately and aggressively. To suggest that someone can't be allergic to it is to show that they are completely ignorant of how allergic response works and also that they're almost certainly a selfish smoker who doesn't want to face the fact that their chosen habit affects other people so badly.

Don't know why this is getting voted down. The data are in: lung cells begin to change the moment they are exposed to smoke. It's one reason why smoke is such an effective (and addictive) nicotine-delivery method.

... first, it took me three times to even figure out what you were saying, second, while it's unlikely people are allergic to cigarette smoke in the traditional sense (ie, allergic to everything that makes up cigarettes), I personally am allergic to tobacco, as in, it's a tested allergy. I'm also asthmatic. This means I do my best to hold my breath if I can't avoid walking past someone who's smoking. I don't expect people to not smoke in public if it's not sign posted not to, but at the same time, yelling at someone for coughing (not for insulting their habit or making rude gestures at them, merely coughing) is immature and ridiculous.

1) Punctuation. It's your friend. 2) Why would OP feel the need to lie to the readers of some website?