Sunglasses should be replaced every 2 years, otherwise it’s the same as not wearing them?

gossip

“Do I need to replace sunglasses every two years?”

Some people on the Internet say that sunglasses also have a lifespan and need to be replaced every two years.

Rumor Analysis

This statement makes sense to a certain extent, but it does not fully conform to national conditions and needs to be adjusted.

Sunglasses do have a lifespan, because the sunscreen material will age, and the sunglasses themselves will become loose and damaged. However, in China, it is not necessary to replace sunglasses every two years. It is not too late to wear them for another one or two years.

Midsummer is here, the sun is scorching, and as people's health awareness increases, more and more people wear sunglasses when they go out. For many friends, the reason for replacing sunglasses is mostly because they are broken, lost, or not fashionable enough... But in fact, there is another important reason that is often overlooked, that is, the sunglasses are "aging and ineffective" .

Recently, we often see some articles reminding people that "sunglasses only have a lifespan of two years and need to be replaced when they reach that age." So, is the lifespan of sunglasses really only two years?

Too long to read

The UV protection of sunglasses will indeed gradually decrease with use, and it is necessary to replace them.

But for most people in my country, it is not necessary to replace it every two years. Let's talk about it in detail.

Sunglasses really age

The basic material of the sunglass lens itself can absorb some ultraviolet rays, and the coating of the sunglass lens can also reflect some ultraviolet rays. Many sunglass lenses also add materials that absorb ultraviolet rays. In this way, most ultraviolet rays can be "kept out" and no longer harm our eyes. However, this protection is not permanent .

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Because ultraviolet rays carry high energy, they will age the materials of sunglasses and reduce the ability of sunscreen ingredients to absorb ultraviolet rays. The shiny coating on the outside of sunglasses is actually the result of metal vapor deposition, and these coatings may wear and oxidize, and their reflective ability will decrease. All of these will reduce the ability of sunglasses to protect against ultraviolet rays.

In addition, if we do not take good care of the sunglasses, it will often cause direct wear of the lenses, loose temples, deformation and damage of the frames and nose pads, all of which will affect the normal use and protective effect of the sunglasses.

Is it really necessary to change every two years?

I would like to state here that this is not a rumor, but a real research.

Professor Liliane Ventura and her team at the University of São Paulo in Brazil have done a lot of research on sunglasses. In one of their papers, they did recommend replacing sunglasses every two years. This conclusion has also been cited by many media outlets, and we often see similar content in Chinese today.

But this conclusion actually has a premise, that is, the researchers calculated it according to the working intensity of sunglasses in Brazil ... That is, if you wear sunglasses for 2 hours a day , the UV protection ability of the sunglasses will decrease after two years and should be replaced.

Let's feel it. In Brazil, the sunshine in most places is like this... After all, it is a passionate South American country, and more than half of its land is in the tropics...

João Pessoa in northeastern Brazil under the sun. Image source: Reference [1]

So from this perspective, most people in northern China do not wear sunglasses for 2 hours a day. Therefore, we can save money and wear them for one or two years before changing them according to the frequency of wearing. Some well-known sunglasses or sports sunglasses manufacturers also recommend changing them every 2 to 3 years, depending on the frequency of use.

This will make your sunglasses last longer.

A pair of qualified sunglasses is often not cheap. If we take good care of them, we can make them protect us longer. Specifically, we only need to:

· When not in use, store it in time to avoid wear and tear or direct sunlight.

If you are driving, do not place your sunglasses on the center console to be exposed to the sun.

When temporarily placing sunglasses, make sure the lenses are facing upwards to avoid wear and tear.

Use a glasses case or glasses bag , as these special storage containers have soft interiors that are gentle on the lenses.

Do not put your sunglasses in your pocket or throw them into your backpack to avoid rubbing against other items such as your keys, wallet, or cell phone. This can easily damage the coating on the glasses and may even damage the frame.

When cleaning sunglasses, you can use detergent, hand soap or other cleaning agents to make foam to clean the lenses. After rinsing, wipe them dry with a lens cleaning cloth, or directly use special wet lens cleaning paper. This is less likely to cause scratches than "dry wiping".

Wear sunglasses correctly and don’t place them high on your head , as they may fall off and break, or break the temples.

Just remember these when choosing sunglasses

In fact, it is not difficult to choose qualified sunglasses. You just need to go to regular stores and look for sunglasses with the "UV400" or "UV100% " logo. These two logos indicate that the sunglasses can protect against ultraviolet rays by nearly 100%, which is enough to provide protection. So how should we choose the color? Generally speaking, for daily use, we can give priority to brown and gray lenses, because they have less impact on the color of objects, and are more convenient for daily use, especially driving, and will not affect the driver's observation of traffic lights. In addition, friends who drive can also choose sunglasses with polarized lenses to reduce glare and drive comfortably.

When choosing sunglasses, there is one thing that is easily overlooked, and that is the "shape". It is easy to think that sunglasses with a larger area and a curvature that fits the face shape have the best sun protection effect .

Image source: Reference [2]

If the sunglasses are not the right size, the curvature does not fit our face shape, or the lenses are too small, even if the lenses have qualified UV protection, it is still easy for light to leak everywhere, greatly reducing the sun protection effect.

We often see articles saying that a money detector light + banknotes can determine whether sunglasses are reliable or not. Because sunglasses can block ultraviolet rays, the money detector light cannot illuminate the anti-counterfeiting mark through the sunglasses.

This statement is actually debatable , because it is related to the power and wavelength of the banknote detector lamp. Many banknote detector lamps have low power and fixed wavelength. Some ordinary glasses can block the ultraviolet light emitted by the banknote detector lamp, so that the banknote anti-counterfeiting mark cannot light up. Therefore, it is safer to use professional instruments to judge the protection ability of sunglasses. For ordinary consumers like us, it is most important to identify "UV400" and "UV100%".

To conclude, sunglasses do have the saying of "expiring and deteriorating", but we don't have to replace them every two years.

Looking in the mirror of rumors

When we see a conclusion, we don’t have to use it immediately. It’s better to first look at how this conclusion was reached.

References

[1] Mauro Masili, Fernanda Oliveira Duarte, Christopher C. White, Liliane Ventura, Degradation of sunglasses filters after long-term irradiation within solar simulator, Engineering Failure Analysis, 2019, Volume 103, Pages 505-516,

[2] Backes, C., Religi, A., Moccozet, L. et al. Sun exposure to the eyes: predicted UV protection effectiveness of various sunglasses. J Expo Sci Environ Epidemiol 29, 753–764 (2019).

Planning and production

Author | Dingzhong Science Creator

Review | Jia Changkai, deputy chief physician, Xiamen Eye Center, Xiamen University

Planning丨Ding Zong

Editor: Ding Zong