inhaled corticosteroid
An inhaled corticosteroid delivers an anti-inflammatory steroid straight to the lungs, like applying a calming cream exactly where the irritation is rather than treating the whole body. It does not open the airways on the spot; instead it dampens the underlying swelling and irritability over time.
These steroids (budesonide, fluticasone, beclometasone) enter airway cells, bind glucocorticoid receptors, and change gene activity to reduce inflammatory mediators, cell recruitment and mucus, while restoring the airways' responsiveness to bronchodilators. Inhaling them concentrates the effect in the lung and keeps the dose low, so the serious side effects of long-term oral steroids are largely avoided. They are the cornerstone preventer therapy in asthma.
Because they act on inflammation rather than muscle tone, they must be taken regularly to work and give no quick relief in an attack. Local side effects include oral thrush and a hoarse voice, reduced by rinsing the mouth and using a spacer; at higher doses some systemic effects can appear. The benefit-to-risk balance strongly favours their use in persistent asthma.
A child with persistent asthma uses a daily budesonide inhaler through a spacer and rinses afterwards to prevent oral thrush.
Budesonide reduces airway inflammation locally with limited systemic exposure.
An inhaled corticosteroid is a preventer, not a reliever: taken daily it controls inflammation but gives no rapid help during an acute attack.