【SkinCare 2: Protection is the Key – Basic Knowledge of Sun Cream】

Skin aging is a universal beauty problem all the skincare manufacturers, dermatologists, scientists as well as customers would pay attention to and it is also one of the indicators to define what is so-called “good/pretty” skin.   

To me, good skin needs protection and prevention. When we talk about protection, the first thing I think of is the sun cream and it’s the only skin care product I can’t skip in my skincare regime and will apply more than once daily in both indoor and outdoor.

As we know, UV radiation is the key killer of skin aging problem apart from other factors like the changes of hormones and metabolism, etc. 

Then how should we fight with UV radiation when we go out?

As a Chinese motto goes, “In order to win, know your enemies and yourself before getting into any battles.” 

In here, I will share with you some basic knowledge of how UV radiation affects us and what the sun cream product consists of. 

  1. What is UV radiation? And how they affect us? 

Well, before talking about UV radiation, first I would like to focus on is  sun radiation, which consists of 7% UV, 39% visible light and 54% infrared light and we are all exposed to the sun radiation during daytime in both indoor and outdoor.

Image source : Ultraviolet (UV) Radiation

UV stands for “Ultraviolet” and UV radiation is a form of electromagnetic energy from natural source like sunlight and artificial sources such as lasers, black lights and tanning beds. 

In here I am talking about the UV radiation from sunlight with different wavelengths. It varies in the intensity by seasons, locations (which is related to latitude and altitude), Ozone, clouds, reflection factors (like snow, water, sand and pavement) and time of day (10:00am to 4:00pm are the stronger UV ray period). 

It can be classified into 3 types as shown below and all types of UV can cause skin redness, tanning, sunburn, premature aging, skin cancer in different levels based on their own characteristics and energy level

UV-C (absorbed and blocked by our Ozone layer):

Generally, it’s the main factor to cause “Cancer

The wavelength(200-280nm) is the shortest while energy level is the highest, since it is blocked by the atmosphere, we might not be exposed to it. However, UV-C can cause serious damage to all forms of life such as the damages on human eyes and skin like burns, lesions and ulcers, killing the bacteria, etc.

UV-B (5% of UV reach the earth):

Based on its name and for easy memory, B is for “Burning”. However, it can directly damage DNA and cause most skin cancers and contribute to skin aging prematurely in long term. The wavelength(280-320nm) is longer than UV-C but shorter than UV-A with medium energy level. As it is partially absorbed by the ozone layer, about 5% of the UV reach the ground and only stay on epidermis(表皮)layer of our skin. Therefore, it will cause skin reddening, sunburn, blistering, free radical(自由基) generation and DNA damage. It triggers the skin’s natural UV-protection by thickening of the stratum corneum (角質層) and the production of melanin (黑色素). In long term, it can cause the most skin cancer and contribute to premature aging. UV-B won’t penetrate windows and are more likely to be filtered by clouds.

UV-A (95% of UV reach the earth)

Generally, it’s main factor to cause “Aging”, the wavelength is longer than UV-B with lower energy level. Unlike UV-B, they’re not absorbed by the ozone layer. About 95% of the UV-A will reach the ground. Therefore, an immediate tanning effect, and sometimes a sunburn will tend to appear right away. It can be divided in to 2 types based on the wavelengths: UVA1 (340 and 400 nm), UVA2 (320 and 340nm). It can penetrate deeply and reach the dermis(真皮) layer of skin, causing photos aging(光老化) and DNA oxidation(基因氧化) in long term. Collagen is found in the lower part of dermis(真皮) and its main function is to give elasticity and hold the skin together. When the elastin starts breaking down, the body produces enzymes called metalloproteinases(金屬蛋白酶, MMP), which further contribute to collagen breakdown and wrinkles and sagging will be caused. Recent research has confirmed that UV-A damages skin cells called keratinocytes(角質形成細胞) in the base layer of the epidermis(表皮), where the majority of skin cancers occur. Therefore, protection from UV-A become important gradually. It can penetrate windows and clouds. Therefore, even though we stay in indoor, we still need to apply sun cream to filter the UV-A. 

Apart from UV radiation, there are 2 types of lights from the sun would also cause photo aging problem. They act as support wings for UV-A to further skin aging problem. They are as shown below.

Image source : The Sun’s Rays and Skin Damage

Visible Light (39% of sun radiation):

Among the visible lights, blue light is the shortest wavelength with highest energy level. We are not only exposed to it during day time but also from artificial sources such as fluorescent lights, computer monitors, smartphone screens, televisions and other digital devices. Comparing with UV radiation, blue light penetrates the skin more deeply into the dermis(真皮). It can potentially generate free radicals(自由基)  (known as reactive oxygen species活性氧化物, or ROS), which cause skin cells to produce enzymes that destroy the collagen and elastin in the process called oxidative stress, lead to premature aging and discoloration in skin. It is also efficient at inhibiting melatonin(褪黑激素), a hormone that regulates the circadian rhythm, which is the body’s natural clock. Therefore, excessive use of screen devices, especially before bedtime, can lead to changes in sleep patterns and result in less quality sleep. Research also confirmed that blue light can harm our vision, from retinal damage(視網膜受損) in the short term to macular degeneration(黃斑部退化) in the long term.

Infrared Lights (45% of sun radiation)

They are the longest wavelength with the lowest energy level of the sun radiation. It is divided into 3 categories: IRA, IRB and IRC. Unlike IRB and IRC, IRA penetrates deep into the skin (2/3 reach the dermis真皮). However, comparing with UV-A, the underlying mechanism of IRA is different. UV-A generates free radicals(自由基) directly in the cell membrane(細胞膜)while IRA induces their formation mainly in the mitochondria(粒線體) which provides cellular energy, signals, cellular differentiation, cell death, maintaining control of the cell cycle and cell growth. Therefore, IRA can be considered as an important contributor to the photo-aging process and cause the appearance of wrinkles, age spots and discoloration and makes the skin lose its firmness and elasticity. Research confirmed that sun cream filters may only protect skin from up to 55% of free radicals(自由基). They couldn’t filter or reflect IR radiation. Therefore, if our skins don’t have enough antioxidant capacity to eliminate these free radicals(自由基), the existing collagen will be damaged and not sufficiently replaced as the production of new collagen is reduced.

Conclusion

Based on the above explanations, skin aging problem is attributable to the causes of both natural and artificial lights in both indoor and outdoor. While UV-A, visible lights and infrared lights are mainly for skin aging, UV-B is mainly for DNA damages and skin cancers. If we want to protect the skin from sun damage and photo-aging, we need to choose the products to filter both UV-A, UV-B with enough antioxidant ingredients to eliminate the free radicals.

2. Basic Principles of UV-Filter Action

In the market, there are 2 types of sun cream product classified by the active UV filter ingredients. They are

Organic UV filters (Chemical) through scatteration and absorption  

It acts like sponge penetrating the upper layers of the skin and converts the UV radiation into thermal energy. It takes 20 minutes to be effective. Therefore, we have to apply it before going out. Direct light caused the chemicals to be used up more quickly, so re-apply frequently is needed.It is rubbed into the skin easily without leaving a white residue and the texture is light but will clog pores. It might trigger an immune response and cause irritation, itchiness, or an allergic reaction. It will be absorbed in the body, leave in blood and disrupt hormones. Therefore, pregnant women and nursing mothers are not recommended to use.

Most of the chemical filters protect against UV-B, and few of them also protect against part of the UV-A range

Inorganic UV filters (Physical) through reflection 

It acts like a mirror to deflect the UV radiation. It will be effective after being applied immediately, no need to wait. It will not clog pores, tend to have a white residue and can be visible on the skin. It can be rubbed, sweated, or rinsed off easily, which makes frequent reapplication. However, today’s 2 approved mineral filters such as zinc oxide (filter UVA1, 2 and UVB), and titanium dioxide (filter UVA2 and UVB) have nano versions. They don’t leave any trace but of course, there are some searches on their negative impacts on health and environment, if you feel interested, you can read the below links or search online for more information.

Extra reading:

  1. Mineral Sun Cream: The Better UV Protection?
  2. How safe are zinc oxide and titanium dioxide?
  3. What is organic & inorganic sunscreen?

These 3 articles raised out 2 interesting points

  1. Both zinc oxide and titanium dioxide in their ordinary or nano versions are known asphotocatalysts(光觸媒、光催化劑) that can form free radicals (自由基) which can damage your cells and DNA. In order to solve this problem, you need to have sufficient antioxidants in your skin to eliminate them or manufacturers need to use “coated” zinc oxide and titanium particles. 
  2. Any physical sun cream is translucent or quite translucent, always uses nano particles. Nano-titanium dioxide can penetrate the dermis while nano-zinc oxide penetrates no further than the epidermis(表皮).

Therefore, if you ask me which one is better for human and environment in general? 

I will just say nothing is perfect. Choosing a sun cream for yourself is a personal preference, you have to take skin type, texture, your existing body and facial situation into consideration. 

If your skin is sensitive and you are pregnant or breast-feeding, comparatively a physical sun cream would be the choice as it is less likely to cause irritations and be absorbed by body.

And the most important thing is that you need to go for the one you will use frequently because sun cream is not like other skin care products under the cosmetics regulation, it is requested to guarantee the skin protection performance.

In some countries such as the US, China or Canada, sun cream is classified as over the counter (非處方, OTC) product, which is required the pre-market registration to make sure the protection claims have been guaranteed. 

Therefore, you don’t need to worry about the safety too much because sun cream in global compliance limits the choices of UV filters in formulations and the product choices you can pick.

For example, US, Europe, China, Japan, Korea and Australia, etc. have their own approved UV filter list. They will review and test those ingredients regularly on their safety and effectiveness and rule out the result for public reference. 

Therefore, some ingredients might not be allowed in some countries but will be allowed in others. For example, there are currently 44 approved UV filters in Europe16 are approved in the us (sun cream ingredients) and 27 are in China

Based on the above numbers, when it comes to sun cream technology development and approval, Europe, Asia, Canada, and Australia seem to be ahead of the US. Many of them are not approved by the FDA or some will slowly be approved in the coming years. 

In addition, advertisers will also reinforce the market trend and have impacts on product diversity. So you can see physical sun cream become the star in recent year and almost every brand launch their own physical sun cream to cater the market needs.

But again, think wisely, before making any purchases, doing some researches online and read the full ingredient list carefully. Don’t be affected by those ads and the reviews from others because something look good on others might not suit you. 

3. The Common UV Filters

If you read【SkinCare 1: The Types of Ingredients】, you will know what consist of a facial cream in general. For sun cream, the formulation will be similar. Below are the typical components of a sun cream formulation with SPF 30 for your reference. 

Image source : What is a sunscreen cosmetic product made of?

However, different UV filters perform differently. Below are the commonly used UV filters for UV-A1, UV-A2 and UVB approved by the FDA for your reference. 

Europe: European Chemicals Agency

USA: Food and Drug Administration

China: National Medical Products Administration

Some of the UV filter names above might be presented or displayed differently with the INCI names on packaging. If you want to find out their official names, you can visit the below links. 

USA: Personal Care Products Council

Europe: European Commission

Based on what I have consolidated from some of the research results above, you will find that quite a lot of ingredients have been classified as toxic or dangerous.

However, as I have mentioned before, the government has regulated all ingredients in the product with a quantity and dosage that does not cause a threat to human health. Therefore, the above list is just for you to know which ingredients can filter UVA or UVB or both so that you can know how to category and choose sun cream. 

In order to optimize the effectiveness and texture of a sun cream product, chemists will mix multi-ingredients together and we can categorize them into 3 types:

  1.  Chemical

Based on the above table, there are only Avobenzone and Zinc Oxide can filter UV-A1. However, Tinosorb S, Tinosorb M (these 2 are not approved by the FDA, but available in other countries) and Mexoryl SX (approved by the FDA and patent held by L’Oréal and its brands) can also filter UV-A1 and UV-A2. What I want to say is that any sun creams include Zinc Oxide will not be pure Chemical sun cream. So if you are looking for Chemical, please look at the full ingredient list first. 

Sensitive, rosacea-prone skin(玫瑰痤瘡肌), as well as for individuals with hyperpigmentation(色素沉澱) might not be suitable due to the heat-releasing nature of chemical sun cream and the heated skin might cause an increase in existing brown spots. 

2. The Combination of Chemical and Physical

Most of the chemical UV filters protect against UV-B with great performance, and few of them also protect against part of the UV-A range. If chemists want to combine the benefits from chemical and physical UV filters, they will add either Zinc Oxide or Titanium Oxide with some chemical UV filters to create a better user experience:  less likely to cause skin irritation, less visible on face with high performance.

3. Physical

Zinc Oxide and Titanium Oxide are the only two active physical UV filters approved right now and only Zinc Oxide can filter all UVA and UVB.

Titanium Oxide only can filter UV-A2 and UVB but not UV-A1, so if a sun cream only includes Titanium Oxide, its coverage is not comprehensive and good enough. So you should look at Zinc Oxide on its ingredient list. If no, then some chemical UV filters might be added in order to fulfill the protection requirement. 

Nowadays, based on the concerns of human’s well-being and environment protection, type 2 and 3 are the dominant categories in the market. However, if you want to find a “pure” physical sun cream, please find the presence of Zinc Oxide in the ingredient. 

Extra readings:

  1. The ABC’s of Ultraviolet Radiation
  2. Ultraviolet (UV) Radiation (American Cancer Society)
  3. UV Filters Chart: Sunscreen Active Ingredients
  4. Sunscreen FAQs (American Academy of Dermatology Association)

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