The allergies vary with the individual and other factors, and usually don't occur until one has had repeated exposure. I had no problems until about two years after I started with photography. Then I started getting mild bumps in the same spots every now and then. Each time it gets worse too. The older doctor (UCLA dermatologist) I talked to was familiar with this, as, of course, lots more people used to work in darkrooms so these complaints were not all that uncommon. He said, like poison oak and poison ivy, you become more allergic the more exposure you get.
Simple solution: just wear gloves. It has worked so far with me!