I am allergic to phenylenediamine and some color developing agents. Once you become sensitized to one developing agent you often become cross-sensitized for other ones. This is why I always discourage people from using ppd based developers. IMO, this developing agent is not necessary for todays finer grained emulsions.
A researcher in organic mercury compounds died a few years ago. She thought that her gloves would protect her and didn't immediately remove them after a sihgle drop of methyl mercury contacted one of them.