Due to skin excretes an oily mixture that make your metal frames slippery and dirty. To prevent this grime to prevent damage to your glasses, you should wash your glasses weekly. Firstly, let your metal frames sit oversight in a glass of lukewarm water with dish soap. The dish soap will break down oil and grease from your skin, whereas hand soap may not. This step is important as it removes dust and grime as well as body oils, all of which combined can result in scratches on your lenses. After you remove your soaked lenses, rinse them in warm water to flush away the broken-down grime. You can then dry them with a soft towel. Do not use a paper towel or tissue, as they tear apart and leave fibers on your lenses. Make sure the towel is clean and as soft as possible. Special eye-cleansing cloths are available at most pharmacies or shopping centers and are relatively cheap.