Have a boil on penis when is safe to have sex?

Get tested and treat: It would be unsafe to have sex until you know and take medicine for your symptoms. Would probably need both skin culture testing and lab and urine tests. I also would recommend routine STD testing/screening to keep you and your partner(s) safe in future.

Here are some ...: Let commonsense rule our life; no sex until the boil is drained, subsided, and healed. If this boil is recurrent at the same spot, surgical complete removal of the affected sebaceous cyst usually under local anesthesia is advised.

Go see the Doctor: There is a common problem called a sebaceous cyst that is not an infection and not a boil. A boil, a pus filled irritated lesion, is usually an infection and requires treatment. If the 'boil' does not hurt then we may worry this is syphilis. Any way all of the above conditions need to be diagnosed by a physician with an examination.