Hydrocortisone is a steroid medication that treats inflammation in the body. The drug comes in an oral form to take by mouth, and a topical form to apply to the skin.
Some kids ask to be left alone as early as 5 or 6; others enjoy having your company until they start approaching puberty, closer to 9 or 10. Bathing alone, however, can be risky because of drowning dangers, and it can take just a few seconds for even older kids to slip and drown in only a few inches of water.
I am weighing that decision myself. I think that 5 is probably old enough to do it himself with your supervision. But, I am a nervous ninny and wouldn't feel comfortable being too far away. Maybe there is something you could be doing in the bathroom while he is bathing.