There is little evidence as to what percentage of a topical corticosteroid dose is absorbed systemically. Studies investigating systemic effects do not measure how much of the corticosteroid is in the blood, but instead focus on measuring cortisol as a marker of hypothalamic-pituitary-adrenal (HPA) axis suppression. After a few weeks’ treatment with potent or very potent topical corticosteroids temporary HPA axis suppression does occur. However, this resolves upon cessation of the topical corticosteroid, without the need for dose tapering. 5, 19 HPA axis suppression is more marked when topical corticosteroids are applied under occlusion, . with wet wraps.
Corticosteroids have been used as drug treatment for some time. Lewis Sarett of Merck & Co. was the first to synthesize cortisone, using a complicated 36-step process that started with deoxycholic acid, which was extracted from ox bile .  The low efficiency of converting deoxycholic acid into cortisone led to a cost of US $200 per gram. Russell Marker , at Syntex , discovered a much cheaper and more convenient starting material, diosgenin from wild Mexican yams . His conversion of diosgenin into progesterone by a four-step process now known as Marker degradation was an important step in mass production of all steroidal hormones, including cortisone and chemicals used in hormonal contraception .  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.
Topical corticosteroids are available in a wide range of different strengths, from Class 1 (very strong) to Class 7 (very weak). Stronger corticosteroids are generally more effective in reducing moderate to severe symptoms, such as thick, chronic plaques, but are also more likely to cause side effects 2 . Lower strength corticosteroids are generally better for milder symptoms and for very sensitive areas of the body (such as the face or groin areas) and stronger strengths are better for areas with thicker skin (such as the knees and elbows).