Here is the materials information from Apple:
Important safety information for Apple Watch - Apple Support
From that: Apple Watch models with a stainless steel or aluminum case, the stainless steel portions of some Apple Watch bands, the metallic portions of Hermès bands, and the magnets in the watch and bands contain some nickel. Nickel exposure from these materials is unlikely, but customers with known nickel allergies should be attentive when wearing them until they can determine they are not experiencing an allergic reaction.
As for allergies and dermatitis, best check for recommendations from your preferred medical provider.