Steroids, known medically as corticosteroids, can reduce inflammation associated with allergies. They prevent and treat nasal stuffiness, sneezing, and itchy, runny nose because of seasonal or year-round allergies. They can also decrease inflammation and swelling from other types of allergic reactions. Systemic steroids are available in various forms: as pills or liquids for serious allergies or asthma, locally acting inhalers for asthma, locally acting nasal sprays for seasonal or year-round allergies, topical creams for skin allergies, or topical eye drops for allergic conjunctivitis. Steroids are highly effective drugs for allergies, but they must be taken regularly, often daily, to be of benefit -- even when you aren't feeling allergy symptoms. In addition, it may take one to two weeks before the full effect of the medicine can be felt.