How olng does dermatitis ofthe penis last?

Depends...: How long skin inflammation (dermatitis) may last? That would depend on its cause and response to treatment. If related with long foreskin, good hygiene + topical antifungal cream with steroid may improve and resolve in 3-5 days for most of patients although circumcision may be needed for the long-term care of choice. So, be checked for individual need. Best wish to health....