Asthma and obstructive sleep apnea (OSA) are two of the most prevalent respiratory diseases in the world. Their high prevalence increases the probability of the two diseases coexisting by chance in a single individual, but in recent years various studies have also shown a real one-to-one association between them. Source: PubMed. Keywords: asthma (title) and OSA (title) and apnea (title) and positive airway pressure and CPAP (title). All manuscript related to the relationship between asthma an OSA as well as its treatments in terms of pathophysiological, diagnostic, etiological, epidemiological and treatment points. 50% of asthmatic patients suffer from OSA and that the adjusted risk of developing OSA in asthmatics is 2.5 times higher than in non-asthmatic individuals, especially in poorly controlled, more severe or longer-standing asthmatics. Several mechanisms have been postulated to explain this increase in OSA in asthmatics: obesity, gastro-esophageal reflux, rhinitis, nasal polyps, increased pharyngeal collapsibility due to mechanical, inflammatory or dynamic causes and, finally, the upper airway deposition of inhaled corticosteroids (IC) generating myopathy in the pharyngeal muscles (as occurs in the vocal cord muscles, resulting in dysphonia). Although both asthma and OSA are common diseases that can coexist in the same individual, a one-to-one association between the two diseases has been observed. The presence of asthma could generate or exacerbate a pre-existing OSA. Caution is recommended in IC inhalation techniques in patients with OSA. The use of ultrafine particles with less pharyngeal deposition is recommended.