There are two main reasons why clear phone cases turn yellow:

• UV light exposure: Clear phone cases are typically made from a type of plastic called silicone. Silicone is a polymer that is naturally yellow, but it is often dyed blue to make it appear clear. When silicone is exposed to UV light, the blue dye breaks down and the natural yellow color of the silicone becomes more visible.
• Natural oils and sweat: Our skin produces natural oils and sweat, which can also cause clear phone cases to turn yellow. These oils and sweat can seep into the silicone and break down the blue dye.

In addition to UV light exposure and natural oils and sweat, other factors that can contribute to the yellowing of clear phone cases include:

• Heat: Heat can also accelerate the yellowing process. This is why clear phone cases are more likely to turn yellow if they are left in hot cars or in direct sunlight.
• Chemicals: Exposure to certain chemicals, such as chlorine, can also cause clear phone cases to turn yellow.
• Time: Over time, even clear phone cases that are not exposed to any of the above factors will eventually turn yellow. This is because the blue dye in the silicone will eventually break down on its own.

There is no way to completely prevent clear phone cases from turning yellow, but there are a few things you can do to slow down the process:

• Avoid exposing your phone case to UV light: Keep your phone case in a cool, dark place when you are not using it.
• Clean your phone case regularly: Wipe down your phone case with a damp cloth to remove any dirt, oil, or sweat that may be building up on it.
• Choose a phone case made from a different material: There are some phone cases that are made from materials that are less likely to turn yellow, such as polycarbonate or TPU.

If your clear phone case has already turned yellow, there is not much you can do to make it clear again. However, you can try to reduce the appearance of the yellowing by using a UV protection spray or by applying a clear coat of nail polish.