Dyspnea, dyspnoea, shortness of breath, or breathlessness is the feeling or feelings associated with impaired breathing. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity," and recommends evaluating dyspnea by assessing the intensity of the distinct sensations, the degree of distress involved, and its burden or impact on activities of daily living. Distinct sensations include effort/work, chest tightness, and air hunger (the feeling of not enough oxygen).