Pastic frames sliding down the nose

I had a question on SF

I find that in the summertime my sunglasses slide a bit on my nose; is there anything I can put on the bridge to stop this? It is because of sweat/grease; they are fine in the winter time.
-Biscotti

There may be several reasons.

1. They dont have any nose pads (only molded plastic) which will not allow them to grip.
Remedy: there are small rubber pads that you can put on them to prevent them from sliding. (think "hotel bathtub")

2. Poor fitting. They may not be tight enough
Remedy: Take them into an optical and ask them to adjust them. They may be too loose, but keep in mind that if they are too tight, they will hurt behind your ear.

3. Wayfarers in general do not fit well on many people. They have way too much pantoscopic tilt for them to be comfortable. (the angle at which it sits on your nose)
Remedy: an excuse to buy something new

4. Oil from your faces are making them slide.
Remedy: try cleaning the nose bridge occasionally to remove excess oil. You'll find that they instantly "stick".

Easiest option: 4
Best option: 2 after doing 4