CRP and inflammatory response: Although in vitro and animal studies indicate that there are respiratory irritants in e-cigarette liquids capable of eliciting pulmonary inflammation, especially at high wattage, other parameters such as the fraction of exhaled nitric oxide (FeNO), a noninvasive marker of airway inflammation, and serum C-reactive protein (CRP), a nonspecific marker of systemic inflammation, are minimally affected by exposure to e-cigarettes [118,119].