Corticosteroids are often called steroids and the most effective anti-inflammatory medicines for the treatment of some allergic disorders Corticosteroidssuch as rhinitis, asthma. Following an allergic reaction different cytokines  and chemokynes, which are responsible for prolonging the immediate inflammatory responses are released.
These are small inflammatory proteins which serve  as messengers to recruit other cells in to the reaction. Corticosteroids prevent the body from making these chemical messengers. 
These are currently  the first line treatment in persistent moderate to severe asthma and very effective for the management of moderate intermittent and persistent allergic rhinitis, eye symptoms, polyposis and sinusitis. Inhaled corticosteroids (ICS) are the most effective controller medications in asthma available worldwide. With the recommended dose of ICS there is no or minimal side effects and no long term effect on growth retardation in children is observed.
In certain circumstances for achievement of maximum clinical outcome in controlling the symptoms and reduce the increased dose of ICS add on therapy with another class of controller medication such as long acting beta agonist and montelucast is recommended.
These  are available in various forms such as such as inhaler, spray, cream ointment, systemic such as tab injections. Systemic (oral ) corticosteroids is recommended    for short term management of acute exacerbations of  asthma, and in combination of other disease such as rhinitis and eczema.
However, long term use of steroid in high doses may have adverse effect though it may be needed for severely uncontrolled asthma. However, these patients should follow up closely  for the adverse effect  such as thinning and bruising of skin, swelling and red face, peptic ulcer, diabetes, muscle weakness, cataract, osteoporosis and growth retardation in children.