For safety reasons, it's recommended that the person giving the hand job removes any rings or jewelry that could injure the penis. Using a condom adds an extra level of safety by preventing the spread of any infections that could be transmitted through bodily fluids, sores or cuts.
It is possible, though unlikely, to get a sexually transmitted disease from a hand job if semen or vaginal secretions come into contact with the genitals or an open cut. Dirty hands can also spread germs or bacteria, so it is a good idea to wash hands before and after sexual contact.
