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While not a traditional allergen, cigarette smoke is often an irritant for people with asthma and allergies. Secondhand smoke, which irritates the already inflamed bronchial passages in asthmatics, can cause asthma attacks and worsen the severity of the attacks, according to the Environmental Protection Agency. Moreover, studies have shown that "exposure to tobacco smoke has incredible impact on increasing risk of asthma in kids," Bassett says. So allergists recommend that parents avoid smoking around children altogether, both at home and in the car. It's thought that because kids are still developing, they're more susceptible to the effects of smoke, and they may breathe more rapidly, causing them to take in more smoke than adults.