I applied 0.5 hydrocortisone cream to my to the head of penis, pubic area and scrotum and now the head of penis and scrotum feels somewhat numb. Help?

Unusual. 0.5% Hydrocortisone is really too weak since even 1% is usually not potent enough. If the problem is persistent, you need to stop using it or perhaps try switching to an ointment. See a doctor if the problem fails to resolve or the numbness lasts more than a couple of day. Make sure that the cream does not have a local anesthetic mixed with it.
See answer . There is nothing in Hydrocortisone that is going to cause numbness. Possibly related to underlying dermatitis or your overall anxiety and perception/concerns regarding the current problem. Numbness is not an indicative sign of anything particularly serious in those areas, just a sensation. If you remain concerned and/or your condition worsens, then you should seek prompt and proper medical care.