It is generally not recommended to go to sleep wearing a chain.\
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Chains made of 999 and 916 gold are relatively soft and may get damaged if worn during sleep, as one tosses and turns. This is especially so for chains with more intricate designs and delicate linkages.\
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While the possibility of damage applies to 18K/14K/10K gold chains as well, the risk is lower as the material is harder and more durable. However, fine chains may still break if they get caught in your sleep, or could get tangled if they are too long.