There is one known problem with developer: it can harm your skin. I suffered from quite serious damage to my hands when I was young and too stupid to wear gloves.
The dermatologist who treated me, explained that it's an allergic reaction and different people are sensitive to different developers. Being in London, though, he saw a substantial number of people who worked in darkrooms at that time (late 'sixties). I started wearing rubber gloves and haven't had a problem since, despite making many thousands of prints and developing an awful lot of film.