Systemic corticosteroids (CS) should be considered as first-line treatment for acute asthma exacerbations, especially severe exacerbations. They may sometimes require a few hours or more to achieve their maximum effect. This time delay observed between administration of CS and improvement in lung function or hospital admissions is consistent with the belief that these effects of CS, involving the modification of gene expression, occur with a time lag of hours or days (genomic effect). On the other hand, CS also have effects initiated by specific interactions with membrane-bound or cytoplasmic receptors for CS, or nonspecific interactions with the cell membrane, with a much more rapid response (seconds or minutes; nongenomic effect). This review analyzes the clinical evidence regarding the use of inhaled CS in acute asthma patients, according to the characteristics of the nongenomic effect, and presents a proposal for the use of inhaled CS as a rescue medication in the emergency-department setting.