Hello everyone, my name is Zihao Chen and I am a sunscreen advocate. I am here to explain to you all the significance of wearing sunscreen and how to select your sunscreen. After all, our skin protects us and protecting our skin is important.

Introduction:

There are many harmful things in the world. Ultraviolet rays are one type of them. Light is a form of radiation. Because of the ultraviolet ray’s energy, being exposed to the light outdoor for a long time makes our skin age prematurely.

While the atmosphere is able to block most of the harmful rays with her ozone shield, some of the sun's rays still reach us. The two most common and harmful sun rays are called ultraviolet A (UVA) and ultraviolet B (UVB).

While Ultraviolet A has a wavelength that is shorter than visible light, the wavelength of Ultraviolet B is even shorter. But because UVA ray interacts with water in a unique way, UVA ray is more penetrative despite having longer wavelength than UVB (Chris).

Why does the Ultraviolet A and B rays give us wrinkles and tans?

• Ultraviolet A causes tans tans and photoaging.Tanning happens because the skin is trying to prevent more DNA damage by darkening in an imperfect way. These permanent DNA damage also leads to wrinkles. This is why getting tanned is bad for your skin.
• Ultraviolet B is not as common as Ultraviolet A. However, because ultraviolet B is less penetrative than UVA, it can be blocked by glass. However, in addition to tans, wrinkles, and skin cancers, UVB can also give you sunburn. 

Here is a 69 year old driver who drove for 29 years. Because the left side of his face are always exposed under the ultraviolet rays, it has more wrinkles than the other side. This is why sunlight is bad for us.

Therefore, to protect ourselves, we should wear sunscreen to block both UV rays, a sunscreen that offers broad spectrum protection.

How much protection a sunscreen offers is measured in Sun protection factor (SPF).

The blue lizard sunscreen in this image, for example, has 30+ SPF. 30 SPF means that only 1/30th of the UV rays will reach your skin.

Common Myths:

• Many people believes that a glass panel or clouds can protect them from all UV rays. However, 95% of the UV rays that reaches us are UVA rays, and UVA rays can penetrate clouds and glass. They also remain relatively the same intensity throughout the day.
• Some people are also mistaken that sunscreen last a whole day. However, Sunscreen wears off after two hours or after shower. One teaspoon of sunscreen, which is about the size of four pennies, is enough to protect your face and neck (Staff).

Besides looking for 30+ SPF and Broad Spectrum, how do we choose sunscreen?

Currently there are two ways to block the sunray:

1. Absorbing the UV rays. 
2. Reflecting the UV rays.

The most common mineral ingredients in sunscreen used to reflect the sun is:

• Zinc Oxide 
• Titanium Dioxide.

These nanoparticles acts like a tin foil to reflect and prevent ultraviolet rays from reaching you.

While the ingredients for the mineral sunscreens are not harmful, chemical ingredients that absorbs sun rays are. Some chemical ingredients that absorbs sun rays, such as oxybenzone, penetrates through your skin and interacts with your hormones.

• Researchers found that American adolescent boys who are exposed to oxybenzone, a common active ingredient in absorptive sunscreen, had significantly lower testosterone after an evaluation of CDC exposure data (Ewg).
• A research from the University of Zurich also detected at least one sunscreen chemical in 85 percent of Swiss women breast milk samples, indicating that newborns and fetuses are exposed to these chemicals (Ewg).

Some of these chemicals ingredients undergoes chemical changes after absorbing sun rays, causing their effectiveness to degrades faster than mineral ingredients over time.

Therefore, always look for sunscreen with mineral active ingredients, like zinc oxide.

Summary:

All in all, It is important to wear sunscreen with broad spectrum protection and SPF at least 30 to prevent photoaging, sunburn, and skin cancer since UV rays causes DNA damage in skin cells. It is also important to pick your sunscreen based on active ingredients. Absorptive ingredients such as Oxybenzone are bad but mineral ingredients such as zinc oxide and titanium dioxide are safe.

Citation:

• Chris. “Why Does UVA Penetrate Deeper than UVB, Though It's Weaker?” Biology Stack Exchange, biology.stackexchange.com/questions/69470/why-does-uva-penetrate-deeper-than-uvb-though-its-weaker.
• Staff. “Sunscreen Myths – Debunked!” Blue Lizard® Australian Sunscreen, www.bluelizard.net/blogs/news/sunscreen-myths-debunked.
• Ewg. “EWG's 2018 Guide to Safer Sunscreens.” EWG Tap Water Database, www.ewg.org/sunscreen/report/the-trouble-with-sunscreen-chemicals/.
  

Citation for Images Used:

• Figure 1: https://www.colorescience.com/learn/how-does-sunscreen-work-to-protect-your-skin
• Figure 2: https://www.colorescience.com/learn/how-does-sunscreen-work-to-protect-your-skin
• Figure 3: https://international.sawyer.com/understanding-uva-uvb/
• Figure 4: https://otclabels.com/lib/otc/otc-meds/blue-lizard-sensitive/
• Figure 5: https://www.dermaessentia.com/what-are-physical-and-chemical-sunscreens/
• Figure 6: https://www.researchgate.net/figure/The-penetration-of-UV-rays-into-the-materials-Without-A-and-with-B-UV-shielding_fig6_311953073
• Figure 7: https://www.madesafe.org/toxic-chemicals-in-sunscreen-safer-alternatives/
• Figure 8: https://www.soleoorganics.eu/index.php?route=information/tt_blog&tt_blog_id=1 https://otclabels.com/lib/otc/otc-meds/blue-lizard-sensitive/