Solid gold will not tarnish the way some metals do, but 14-karat or 18-karat jewelry may show oxidation, depending on the alloys used. Clean off residues from lotions, soaps, and body oils by swishing gold jewelry in a bowl of warm water with a drop or two of hand dishwashing detergent added. An old toothbrush comes in handy for gently cleaning intricate pieces, such as link bracelets. Rinse well and dry with a clean, soft cloth or chamois.
Avoid using any product containing chlorine bleach while cleaning gold; chlorine will cause gold to deteriorate over time. Don’t go into swimming pools or hot tubs without removing gold jewelry because the water is likely to be chlorinated.
Reference:
Jeff Bredenberg, editor, in Clean It Fast, Clean It Right: The Ultimate Guide to Making Everything You Own Sparkle & Shine.