Here's a quick and handy tip I picked up for those with nickel allergies: use several layers of nail polish to cover a button or a clasp which causes irritation.

There are people who develop rashes and irritation upon contact to certain metals, particularly those containing some amount of nickel. Unless otherwise specified, nickel is commonly found in jewelries, belt buckles, zippers, clasps, buttons, and even frames of eyeglasses. For those with sensitivities to nickel, a few strokes with a clear nail polish can prevent the metal from getting in contact with the skin, and thus prevent trigerring an allergic reaction.