THE SCIENCE OF SUNSCREEN

Sun protection is an essential step in our skincare routine to safeguard our skin from the harmful effects of ultraviolet (UV) radiation. Given that the southern and central regions of Vietnam are currently experiencing the hottest periods of the year with high UV radiation levels, this post aims to explore the science behind sunscreen and provide guidance on selecting the right sunscreen for your skin.

Let's explore the fascinating world of sunscreen together over a cup of tea!

THE SOLAR SPECTRUM AND HOW SUNLIGHT DAMAGES OUR SKIN

Sun exposure indeed offers various benefits, such as promoting vitamin D synthesis, improving immune system response, enhancing cardiovascular health, treating certain skin disorders, and boosting overall well-being and mood. However, it is important to acknowledge that sunlight can also cause potential damage to our skin, resulting in aesthetic concerns and health issues.

The first thing I would like to mention is what the solar spectrum and wavelength are. So the solar spectrum is like a collection of different types of light that the Sun sends our way, including ultraviolet (UV), visible light (the light we can see), and infrared (IR). When it comes to wavelength, we’re basically talking about the length between the peaks or valleys of these light waves, which help us understand the different characteristics and properties of light.

Now, let's take a look into the details of the solar spectrum and the effects of its different wavelengths on human skin.

• UVC (100-280 nm) radiation is the shortest wavelength among ultraviolet rays and is extremely harmful to the skin. Fortunately, UV-C radiation is largely absorbed by the ozone layer in the Earth's atmosphere.

• UVB (290-320 nm) radiation has a longer wavelength than UV-C does and is indeed damaging to the epidermis. UVB rays are primarily for causing sunburns and playing a significant role in cell DNA damage as a skin cancer precursor. UVB rays are more intense during midday and summer months when the sun’s angle is highest.

• UVA (320-400 nm) radiation has a longer wavelength than UVB but is shorter than visible light. It can penetrate deep into the skin, reaching the dermis layer. UVA rays are directly associated with skin wrinkles and skin aging while having an indirect relationship with DNA damage through the generation of free radicals. Unlike UVB, UVA rays are present throughout the day and can penetrate clouds and glass materials. This highlights the importance of UVA protection, even on cloudy days or indoors.

• Visible light or VIS (400-760nm) is the part of the solar spectrum that is visible to the human eye. While it doesn’t cause sunburn or skin cancer like UV radiation, visible light can penetrate deep into hypodermis layers and contribute to photoaging and hyperpigmentation, particularly in individuals with high skin phototypes (IV-VI)*. It can also generate free radicals leading to skin damage.

*Skin phototypes scale known as the Fitzpatrick scale is the classification system that categorizes individuals into different groups based on their skin’s response to sun exposure. Scale is ranging from type I to VI, in which people with darker skin tones and higher levels of melanin in their skin.

• HEV (High Energy Visible) light (380-500 nm), also known as blue light, is emitted by both the sun and electronic devices. Double exposure to HEV light from these sources can have negative effects on the skin. Prolonged or excessive exposure to HEV light during the day can contribute to photo-aging and damage to skin cells. Additionally, exposure to HEV light at night can disrupt the natural secretion of melatonin, which can affect sleep patterns and overall skin health.

• IRA (Infrared A) radiation (760-1400 nm) can penetrate deep into hypodermis and increase the production of metalloproteases MMP-1 and MMP-9, which contribute to the breakdown of collagen and elastin in the skin, leading to the decrease in skin elasticity and firmness. Additionally, IRA radiation can also generate free radicals, which cause oxidative stress and damage to skin cells.

SUNSCREEN AND ITS MECHANISM

In light of the numerous harmful effects on the skin, sunscreen has become one of the trusted companions for many individuals, as it aims to mitigate the damaging impact of sun exposure.

So let’s discover the difference between physical and chemical sunscreens.

Moving on to the mechanisms of action, physical sunscreens create a physical shield on the skin surface that deflects or reflects the UV rays, preventing them from penetrating the skin. On the other hand, chemical sunscreens are absorbed into the skin and convert UV rays into harmless energy.

These two sunscreens provide various pros and cons discussed in the following table.

	Pros	Cons
Physical sunscreens	​Protection from both UVA, UVB rays, and blue light Provide immediate protection upon application thanks to the mechanism of creating a physical barrier on the skin Less likely to cause skin irritation or allergic reactions, being suitable for sensitive skin types Longer shelf-life	May leave white cast and be harder to blend into the skin Thicker chemical texture may feel heavier on the skin Potential for rubbing off and sweating off more easily
Chemical sunscreen	​Easily spread and blend into the skin without leaving a white cast Tend to be more water-resistant, suitable for outdoor activities Often have a lighter and more comfortable texture on the skin​	​Require approximately 15-20 minutes for full effectiveness after application Absorbs into skin, increasing risks of skin irritation and stinging May cause clogging of pores and increased breakouts on acne-prone skin

Zinc oxide (ZnO) and Titanium dioxide (TiO2) are indeed common active ingredients found in physical sunscreens. They work by reflecting UV radiation away from the skin surface, scattering and dispersing UV rays in different directions to diminish their impact on the skin and provide broad-spectrum protection against UVA and UVB rays. Titanium dioxide (TiO2), it is also used as a pigment in makeup products. However, in its original form, TiO2 can generate free radicals (ROS) when exposed to UV light. To address this matter, advancements in technology have led to the development of TiO2 nanoparticles with improved coatings, enhancing the effectiveness of sun protection. Nevertheless, while the use of TiO2 and ZnO nanoparticles offers improved cosmetic spreadability and acceptability, concerns regarding their safety continue to grow. There are ongoing doubts regarding the potential negative effects of nanoparticles on marine animals, environmental producers, skin irritation, and long-term human health.

Avobenzone, known for its photostability mechanism as mentioned previously, is a commonly used chemical filter in sunscreens. This filter is particularly effective at absorbing UVA rays and it is often combined with other chemical filters in sunscreen formulations to enhance its stability and effectiveness.

PARAMETERS TO EVALUATE THE EFFECTIVENESS AND SAFETY OF SUNSCREEN

• Sun Protection Factor (SPF) measures the level of protection against UVB rays. SPF is defined as the following equation:

MED (minimal erythema dose) refers to “the lowest time interval or dosage of UV light irradiation sufficient to produce UV dose or duration needed to produce a perceptible erythema on unprotected skin”. And it is noted that higher SPF values indicate greater effectiveness in preventing sunburn.

• The Protection Grade of UVA (PA) was originally established in Japan to measure the level of protection against UVA rays provided by sunscreen. The PA rating is indicated by “+” symbols, ranging from PA+ to PA++++, with extra “+” symbols indicating higher protection.

The rating system helps customers choose sunscreens that offer effective protection against UVA-induced skin damage, such as premature aging and skin cancer. And it is important to note that PA ratings primarily focus on UVA protection and should be considered alongside SPF ratings, which mainly reflect protection against UVB rays.

• Broad-spectrum protection is labeled on sunscreen if it provides protection against both UVA and UVB rays. Looking for a sunscreen labeled “broad-spectrum” to ensure comprehensive sun protection.

• EcoSun Pass value was originally established by BASF from Germany to assess the impact of sunscreen formulations on the environment. As awareness regarding the impact of sunscreens on ecosystems grows, customers are becoming more conscious of the need to choose environmentally friendly sunscreen products, mainly in the European cosmetic market. This increased awareness has led to a rise in the selection of sunscreens that minimize harm to marine animals, coral reefs, soil, and other components of biodiversity. By opting for eco-friendly options, consumers demonstrate their dedication to biodiversity conservation and environmental protection.

Here is the formula for calculating the EcoSun Pass value:

• "a": ecotoxicological evaluation of the used filter system, double check more in ref (2) a

• ‘SPF’ and ‘UVA‐PF’ were derived from the sunscreen simulator.

The threshold for the evaluation of sunscreen was set to 200 so if the ESP value of sunscreen is greater than 200, the formulation is regarded as ecofriendly.

Additionally, to evaluate the effectiveness of a sunscreen product, there are some other factors that need to be taken into account, including water resistance, photostability for mining their effectiveness when exposed to sunlight, skin compatibility for avoiding allergies, sensitive skin issues, and so on.

Incorporating sunscreen into our daily skincare routine is essential for maintaining healthy and protected skin. By staying informed about the science behind sunscreen and making conscious choices, we can enjoy the benefits of sun exposure while safeguarding our skin's well-being. Remember, protecting your skin from the sun's harmful rays is a year-round commitment. So let's embrace the power of sunscreen and enjoy the outdoors while keeping our skin healthy and radiant.

Chloe.

References:

1. https://www.scielo.br/j/rbcf/a/7rJ9fNhGB5xQBXDdrbs8KjD/?format=pdf&lang=en

2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8248045/

3. https://www.health.harvard.edu/staying-healthy/the-science-of-sunscreen

4. https://www.personal-care.basf.com/ecosunpass

5. https://www.aveneusa.com/sun-introduction

6. https://mandanaturals.com/blogs/news/why-choose-a-physical-sunscreen