It is common for sunglasses to have swear strains, and you need to clean them to aviod lossing the funciton of sunglasses, for example, the sunglasses can prevent UV rays to damage your eyes. The sweat strains could reflect the sunlgiht to produce glare thus you could not have a clear vision or have a blurry vision. Hence, you need to place the sunglasses in warm water, and washing up liquid with a little white vinegar added. And leave for a few minutes then rinse them.
Well, as we know that properly maintaining and cleaning the plastic lenses of sunglasses will make them look better and last longer. No matter fashionable or functional sunglasses, they should not be cleaned with napkins, toilet tissue or paper towels. The reason is that these objects can scratch the delicate plastic, remove the protective UV coating. So when there are some sweet strains on your sunglasses, you should clean them carefully in a right way. First, you should wash your hand so that it can not make your sunglasses be infected. Then you can warm your soft cloth which is used to rap the lenses which have sweet strain on. Remember you should use warm water when you do this. Finally, you can clean your sunglasses with resolution.
To remove the sweat stains from sunglasses, you shall first soak the sunglasses into clean water for about 15-20 minutes. Then try to rub the sunglasses with sunglasses cloth. If it doesn't work, you may have to use some mild soap water to help your clean the lenses. Just remember use sunglasses cloth to clean the sunglasses. Just not wipe your sunglasses with your T-shirt other clothes. It won't cause scratches.
You can just wash the lenses of the sunglasses with the clean water. You can use the hands to wash the stains out of the lenses. You should not use the toothbrush to wash it which may scratch the lenses. However, you could even use a little amount of cleaning agent to wash the stains out of the lenses.