Time to time I get itchy rashes around my joints. I can go a year without it happening. Benadryl (diphenhydramine) helps it to go away. Any ideas what could cause this?

Depends. This could be a reaction to a soap or laundry detergent. You may want to avoid TIDE and ALL. this could also be a sign of arthritis if you have the rash and joint pain at the same time. . Next time you get this rash you should see your medical provider. .