Thanks for your interest in Apple Watch. I thought this might help:
" Apple Watch models with a stainless steel or an aluminum case, the stainless steel portions of some Apple Watch bands, the metallic portions of the Hermès bands, and the magnets in the watch and bands, each contain some nickel. However, they all fall below the strict nickel restrictions set by European REACH regulation. Therefore, while nickel exposure is unlikely to be a problem, you should be aware of the possibility in case you're susceptible to nickel-related reactions."
More information can be found here: https://support.apple.com/en-us/HT204665
If you still have questions, comments or concerns Contact Apple Support.