Sterling silver tarnishes over time especially when it is in contact with chemicals, humidity and sunlight. To avoid silver tarnishing minimize its contact with chemicals (such as cosmetic creams, hairspray and perfume) and store individually in a jewelry box or an airtight bag. Regular cleaning with a polishing cloth is a good way to prevent future tarnish buildup.
Using silver or any metal polishing chemicals is not recommended as they are very harsh on the silver.