Even though topical corticosteroids such as creams or ointments are applied to the surface of the skin, they can still cause side effects . Long-term use or excessive use can lead to thinning of the skin, irritation, dryness, or changes in skin color. If your doctor recommends that you occlude your psoriasis areas -- wrapping them in plastic after applying a topical corticosteroid to boost the effect -- side effects may be more common. More serious side effects may occur with topical corticosteroids if used in high doses for prolonged periods. You may become resistant to the helpful effects of topical corticosteroids over time, too.
In 1952, . Peterson and . Murray of Upjohn developed a process that used Rhizopus mold to oxidize progesterone into a compound that was readily converted to cortisone.  The ability to cheaply synthesize large quantities of cortisone from the diosgenin in yams resulted in a rapid drop in price to US $6 per gram, falling to $ per gram by 1980. Percy Julian's research also aided progress in the field.  The exact nature of cortisone's anti-inflammatory action remained a mystery for years after, however, until the leukocyte adhesion cascade and the role of phospholipase A2 in the production of prostaglandins and leukotrienes was fully understood in the early 1980s.
There is no evidence of safe and effective use of topical corticosteroids in pregnant mothers. Therefore, they should be used only if clearly needed. Long term use and large applications of topical corticosteroids may cause birth defects in the unborn. It is not known whether topical corticosteroids enter breast milk. Therefore, caution must be exercised before using it in nursing mothers. Topical corticosteroids should not be applied to the breasts of nursing mothers unless the mothers instructed to do so by the physician.