Glasses can fog up because of an abrupt change in climate, typically from cold to warm and humid, or from sweat beading on your face during vigorous activities. It is when the moist, humid air condenses onto the cold lenses that the glasses appear foggy. Fogged up glasses are not only an annoyance but also dangerous. Those who ski, drive or operate heavy machinery must make sure that their glasses are clear and they are able to see properly to avoid any disastrous effects.

Choose the right pair of glasses. When selecting a style, pick a frame that does not sit close to your face to allow for more air circulation. If you continuously find your glasses are fogging up, consider styles that are built with air ducts or vents to help eliminate and control any fogging up that might occur.

Spray your glasses with a lens-cleaning solution. Use a soft, scratch-free cloth to work the solution onto the lens. Dry the lenses with a clean cloth.

Use household products to protect your glasses. Some fluids that help to stop fogging up include toothpaste without baking soda, which is abrasive and will scratch your glasses, potato juice, liquid dish soap and shaving cream. Apply the product to your glasses and let it dry.

Wipe off any excess product with a scratch-free cloth. Work in a circular, outward motion and leave a thin film on the lens to prevent moisture from forming on your glasses.

Purchase a commercial anti-fogging product. Items such as C-Clear, the Smith No-Fog cloth and PMI Anti-Fog Spray are specially designed to electrically charge the glasses to prevent condensation and moisture from building up. Apply the product as directed according to the packaging and remove it with the supplied cloth, wipe or towelette. Use a scratch-free cloth if one did not come in the box.

Allow your glasses to acclimate to new temperatures. If you are going from the outside where the air is hot and humid to a cool, air-conditioned building, let your glasses adjust before you wear them. Keep them on top of your head before going outside to cool down your glasses gradually. You can make fogging less of a hassle by preventing any extreme changes in temperature as best you can.

Wear a headband during physical activities in the cold. The headband will soak up the sweat forming on your face.

Wear proper clothes. Be careful not to overdress, as your body will overheat and produce sweat, causing your glasses to fog up. Avoid overdressing your neck, head and face. Wear only the amount of clothing necessary to stay warm.