Gold-filled jewelry components are made with a layer of gold that's mechanically bonded with heat and pressure to another material, usually a base metal which is most commonly brass. Gold-filled jewelry is resistant to tarnishing because the outside layer is actually gold and is thick enough to prevent oxidation of the inner material. The gold content must be at least 1/20th of the total weight, where the gold itself is no less than 10 karat in purity. I prefer to buy 14 karat gold-filled products.
Gold-plated products have a very thin layer (seven-millionths of an inch) of gold. What this means is that gold-plated items, while less expensive than gold-filled, will not last as long. Eventually the thin gold layer may chip or rub off.
Although gold is tarnish resistant, it's still a good idea to give it gentle care. Soap film can build up on the surface of your gold, so jewelers often recommend removing your gold jewelry before showering or using household cleaners. Chlorine may weaken gold and cause it to break. If your gold loses its shine, you might try cleaning it in a solution with a few drops of ammonia, mild detergent and warm water. You may use rubbing alcohol to remove grease and body oil.