The active ingredient present in hydrocortisone is cortisol.  Cortisol is a mild steroid / hormone (a corticosteroid) that the human body creates naturally but can also be produced synthetically for medicinal uses.  Hydrocortisone, a topical cream, is the most common form of cortisol.

When applied 2-3 times a day Hydrocortisone has been proven to alleviate swelling, itching and general skin irritations (some of the most common psoriasis symptoms). It is available by prescription only.

Cortisol seems to be useful for treating psoriasis because of it’s suppressive effect on the immune system.  It signals to the immune system to stop producing T-Cells (which are designed to fight off hostile cells), which in turn brings down swelling.  Excessive T-cell production has also been linked to the scaling that characterizes plaque psoriasis.  Bringing skin cell production under control in this manner most likely helps to eliminate itchiness (pruritus).  Cortisol also regulates some aspects of metabolism, which also may help to suppress skin cell proliferation.

A friend of mine was prescribed hydrocortisone for the some psoriasis breakouts that occur on his forehead and chin. The effect of this topical cream have been a complete clearing of all scales and itching. He also says that he has experienced no adverse side-effects.