Cigarette/cigar smoke, like dust or allergens, acts as an irritant to the inner lining of the nose. The brain gets the signal to sneeze, and voila.
There are two types of secondhand smoke: side-stream smoke comes from the lighted end of a cigarette or pipe or cigar. It’s the legit stuff. Mainstream smoke is exhaled from the smoker.
Secondhand smoke has adverse effects on the heart, can cause other serious issues like bronchitis, damage to blood vessels, increased risk of a heart attack, and can trigger serious asthma attacks. It contains just as many cancer-causing chemicals as “firsthand” smoke.