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Inhaled corticosteroids (ICS) is the cornerstone of any asthma treatment. The commonly used inhaled corticosteroids are fluticosone and budesonide. It is the first drug class given to any person with newly diagnosed asthma. Inhaled corticosteroids acts by decreasing the airway inflammation and thereby preventing the constriction of the airways (bronchospasm). They reduce the production of pro-inflammatory molecules that mediate bronchoconstriction.

Studies show that regular use of inhaled corticosteroids prevents acute exacerbations of asthma and delays the longterm decline in lung function seen in asthmatics. Inspite of the significant short term benefits ICS doesn't change the natural history of asthma. This aspect has lead some physicians to recommed the use of ICS only on a need basis and not regularly in mild asthma. But in moderate and severe asthma, ICS should be used daily. It also confers a protective effect against the long term adverse effects caused by another class of asthma medication called as LABA. LABA is often combined with ICS for moderate to severe asthma.

ICS is most effective in individuals with eosinophilic (a type of cell) inflammation in the airways. Eosinophils are a type of cells present in the blood and tissues and are associated with allergy and inflammation. Response to inhaled corticosteroids is best in asthmatics with excess eosinophils in sputum. In these individuals, sputum eosinophilia directed asthma therapy has been found to be more optimal as it produces less exacerbations and longer symptom free days. Exhaled breath nitric oxide can be used as a biomarker to assess the inflammation in the airways but it cannot be used to direct therapy in asthma.

The adverse effects of ICS include decreased growth in children, increased risk of pneumonia, adrenal suppresion, skin thinning and osteoporosis. Studies also show increased risk of diabetes in adults.Other  adverse effects associated with the systemic steroids do occur if the dosage of inhaled steroids is high.