Hydrocortisone is one of the steroid hormones produced by the adrenal gland (adrenal cortex) which plays a complex role in regulating body functions and without which survival would not be possible.
Used for skin irritations such as exczema. You can buy E45 over the counter, and HC45 is the prescription version containing the avtive ingredient hydrocortisone, which is (or was when I had it) prescription only