Asthma is a chronic inflammatory disorder of airways, characterized by airway hyperresponsiveness that leads to recurrent episodes of wheezing, breathless, chest tightness, and coughing, particularly at night or in the early morning. Nocturnal asthma is not a different condition from asthma and is defined as a variable worsening of asthma at night, in which the mechanisms are not completely understood. It may be driven by circadian rhythms of circulating hormones such as epinephrine, cortisol, and melatonin and neural mechanisms such as cholinergic tone. An increase in airway inflammation at night has been reported. This might reflect a reduction in endogenous anti-inflammatory mechanisms. Other factors that have been proposed as possible causes for overnight bronchoconstriction are interruption of bronchodilator or other treatment, allergens in bedding, airway cooling, supine posture, and gastroesophageal reflux (GER).