Topical steroids work by reducing inflammation in the skin by several different mechanisms of action.
Alter Chemicals That Cause Inflammation
The steroid molecule is transported to the cell nucleus where it interacts with DNA. This interaction causes the cell to make proteins called lipocortins, which then turn off the production of a chemical called arachidonic acid. Without arachidonic acid many chemicals that cause inflammation in the skin and in the rest of the body are not produced, thus reducing inflammation. These powerful inflammatory chemicals include prostaglandins, leukotrienes, and platelet-activating factor.
Constrict Blood Vessels
An immediate effect of topical steroids is to cause the small blood vessels called capillaries to constrict. A section of skin that has dilated capillaries will be red, warm, and swollen. Therefore causing the capillaries to constrict decreases redness, warmth, and swelling.
Change Immune System Cells
Topical steroids also change the function of the cells of the immune system. White blood cells don't recognize foreign cells as well and have a decreased capacity of fight off these foreign cells.