How often should you replace your sunglasses? It's more frequently than you think

Sunglasses should be replaced every two years as they give less protection against UV rays over time.

Sunlight degrades the lenses, making them weaker, Brazilian researchers said.

The study shows sunlight degrades the lenses of shades, providing less effective protection over time so should be replaced at least every two years.

Scientists say lenses may become lighter and so alter the category under which they are classified and also become more brittle, diminishing the impact resistance of lenses.

The researchers called for a revision of standards in testing sunglasses quality and establish safe limits for the lenses' UV filters.

They say the new test would guarantee that sunglasses can be safe to wear for a period of two years for users who wear them for a maximum of two hours a day.

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Boffins called for new tests that would guarantee effectiveness of shades