The single most common cause. Nose pads that sit too far apart don't grip the sides of your nose firmly enough.

If the arms have widened over time or were never quite tight enough, the whole frame can slide forward under its own weight.

If a frame is genuinely a size too big, no amount of adjustment fully solves it -- see our frame size guide.

Skin oils and sweat reduce the natural grip of nose pads and temple tips, especially in warm weather or during exercise.

For frames with adjustable silicone pads, carefully bend them slightly closer together for more grip.

For plastic frames, a hair dryer's gentle heat can make the arms pliable enough to adjust the curve behind your ears.

Inexpensive silicone hook attachments can add grip without any adjustment to the frame itself.