Jewelry can tarnish over time if exposed to water, oil, make-up or sunscreen from skin but can be cleaned with tarnish remover. You can also opt to use mild, non-phosphate dishwashing liquid and warm water to gently wipe tarnished part using cotton swab or soft, clean cloth.
Here are some ways to keep your jewelry from tarnishing:
Clean hands before handling jewelry.
Store in small jewelry pouches or cool dry place such as jewelry box.
Avoid swimming, exercising or showering when wearing jewelry.
Keep clear of other metals.
Polish jewelry when looking dull.