The most important reason is to protect your eyes from ultraviolet light. UV radiation is as damaging to your eyes as to your skin, and can lead to a whole host of serious eye problems after years of cumulative exposure. These include cataracts and macular degeneration. Excessive short-term exposure can lead to photokeratitis, which is basically sunburn of the eyes. If you’re guessing that this is painful, you guessed right!
Sunglasses also reduce glare, and reduce exposure to infrared light, both of which cause fatigue. And they’re helpful for keeping the wind out of your eyes, along with other hazards (bugs, tree branches, etc.). Trail runners, especially, appreciate the physical protection.
Nevertheless, many runners forgo sunglasses, especially during competition. We’d like you to encourage you to join the enlightened, sunglass-wearing minority. You’ll be happy you did.
Sunglasses come in several darknesses, from category 1 (almost transparent) to category 4 (very dark, generally for use on glaciers). The lightest ones are appropriate if you’ll be running at night or on very gray days.
You might also choose photochromic lenses, which darken in response to sunlight. They’re a great choice for do-anything sunglasses.
Regardless of how dark they are, it’s vital that you buy a trusted brand, and one that blocks 100% UV. Sunglasses that block a lower percentage of UV than visible light are actually worse than nothing, because your irises will open up in response to the shade, and will then let in a higher proportion of damaging UV.
Lenses come in a variety of colors, from neutral gray to light yellow to dark amber to rose. The deeper the hue of the lens color, the more it will accentuate contrast in flat light and hazy conditions. This comes at the expense of color neutrality. With deep rose or amber glasses, you’ll get a more distorted perception of the colors around you. Clear and gray lenses preserve color balance, but don’t improve contrast. Ultimately, your personal preference will be the guide here.
Polarized sunglasses cut glare better than any others. They also create some optical effects that you might find distracting. Screens on phones and smart watches can sometimes be very difficult to read through polarized lenses. You’ll have to try polarized lenses to see if they work for you.
Some sunglasses, especially wrap-around styles, inhibit air flow. You may find these more prone to fog up in some weather conditions.
You may want to have some kind of retention strap to keep your sunglasses from falling off. Some are designed specifically for sports and will keep your shades firmly in place.
You should consider lens tissue and lens cleaning fluid. The best products are single-use, pre-moistened tissues. These won’t be contaminated with grit from previous uses, so they’ll be less likely to scratch your lenses. Beware that sunglasses are very easy to scratch. Plastic lenses, or glass lenses that have anti-reflective coatings, are extremely fragile. Avoid using regular tissues. The paper is often somewhat abrasive. Never just wipe the lenses on your shirt. Any fine grit present on your shirt (or the lens surface) will work like sandpaper and carve little scratches in your once-perfect lenses. If you have to clean your glasses but don’t have proper lens tissue, run them under copious amounts of water.
If you wear glasses for astigmatism or nearsightedness, by all means, consider prescription sunglasses. They’ll be doubly useful for driving.
We’re not going to counsel you on esthetics, but we suggest that if you feel good wearing your sunglasses, you’ll be more likely to actually wear them. And we really want you to wear them! So take the time to pick shades that make you look amazing.