Halfway through a summer run, my sunglasses fog up so bad I can barely see the sidewalk. It happened for years, and I tried everything: washing them with dish soap, buying expensive anti-fog spray, running with them on top of my head. Then a cycling buddy told me the trick that actually works, and it costs about two dollars.

Why Sweat Makes Sunglasses Fog

When you sweat, your body heat and moisture rise toward your face. The warm, humid air hits the cooler lens and condenses, forming a fog layer on the inside. The tighter the glasses sit, the worse it gets.

The Cheap Fix That Works

1. Wash the lenses with a drop of dish soap and warm water.
2. Rinse thoroughly so no soap film remains.
3. Shake off the excess water.
4. Dry with a clean microfiber cloth.
5. Before you head out, rub a tiny dab of shaving cream or a bar of soap across the inside of the lenses.
6. Wipe it off until the lenses look clean.

Why This Works

Soap leaves a microscopic film that breaks the surface tension of water. Instead of beading up into fog, moisture spreads into a thin, clear layer. It is the same principle behind commercial anti-fog sprays, just cheaper.

Things I Got Wrong

Do not use too much soap. A little goes a long way. If you glob it on, you get a smeary film that blurs your vision worse than fog.

Do not use toothpaste. I saw that tip online once, and it scratched a cheap pair of lenses. Toothpaste is too abrasive for most lens coatings.

Reapply after washing. The anti-fog layer wears off when you clean the lenses, so refresh it before every sweaty workout.

For the Heavy Sweaters

If your glasses still fog in high humidity, buy an anti-fog wipe made for ski goggles. They are designed for extreme moisture and last longer than the soap trick. Keep a pack in your gym bag.

The No-Fog Adjustment

Push the glasses slightly down your nose to let air flow behind the lenses. Less trapped heat means less condensation. It looks a little goofy, but it beats wiping your lenses every hundred yards.

I ran a full seven miles last weekend with zero fog. The soap trick plus the nose adjustment is my whole summer system now.