What is the best jewelry metal for someone allergic to nickel?

My husband is having issues with his wedding band. It’s tungsten carbide and is supposed to have a very low amount of nickel, however he’s having some sort of allergic reaction underneath his ring. It’s itchy, red, and flaking. The jeweler said it could be from soap and water being trapped under the ring and irritating his skin. So he has been very careful about removing the ring while washing his hands and fully drying his skin before replacing the ring. He doesn’t wear it during showers or even to bed. He let it heal completely from the first reaction but as soon as he put it back on, it was reacting again with his skin. So what are his options? What is the best metal for this allergy?