My husband's doctor put him on steroids for his asthma and we are wondering what exactly they do?

Inflamation: Steroids (cortisone like) are used in inflammatory conditions like asthma. Though in acute asthma you have constriction in the lungs which causes the difficult breathing, steroids are used to treat the inflamation that is going on even when you have no attacks. Their purpose is to reduce the number and severity of his acute attacks.

Membrane stabalizer: Steroids are a large family of hormones that can influence muscle growth,fluid balance, sexual differences,tissue repair,etc.The steroid type he was given is specific to membrane stabilization/repair and mimics natural steroids made by the body.Since asthma episodes reflect some tissue irritation/injury, these help the body repair itself and can reduce the frequency of attacks.