It is virtually impossible to do most BDSM activities without the use of some metal objects. Usually this causes no health issues, however, some metals are known to cause health issues. Among them are:
Metals that usually do not show any issues include:
If you have a reaction to those materials it is usually because they are not pure (i.e. most gold jewelry these days is 10 or 14k, far from the pure 24k) and mixed with other materials that can cause reactions.