Part 1 - a sunscreen guide

Sun protection

Most of us love spending time in the sun and if we enjoy the sun in reasonable amounts, it can give us many health benefits. However, overexposure to UV radiation can not only cause painful red-burnt skin but also more long-term effects such as premature aging of the skin with deep wrinkles and brown spots. Excessive tanning can also cause various forms of skin cancer. To protect yourself against the harmful sun rays, you can minimize time spent outdoors during mid-day hours when the sun is at its highest point, put on a protective layer of clothing and a sun hat, and apply sunscreen to exposed skin. And precisely those - the sunscreen products – we are going to dive into now.

THE HARMFUL UV RADIATION

When we think of sunbathing, our thoughts often drift to a wonderful day at the beach, but as you know, the sun rays are far from just healthy. Sun rays contain various types of radiation that have different wavelengths. Ultraviolet (UV) radiation is invisible to the human eye and can cause different types of skin cancers such as squamous cell cancer, basal cell cancer and various types of malignant melanoma. Sunscreen products provide protection against UVA radiation, with wavelengths between 315 and 400 nanometers and UVB radiation, with wavelengths between 280 and 315 nanometers. The UVB radiation penetrates the outermost layer of the skin and gives us that lovely, or slightly painful, tan. The UVA radiation reaches deeper into the skin layers and can cause premature aging such as wrinkles and brown spots. The Earth's ozone layer gives us (some) protection against the sun's UVB rays, but it does not affect the intensity of the UVA rays.

It is important to protect yourself against both UVA and UVB radiation. Products that are marked with a UVA symbol have a UVA protection of at least 1/3 of the labeled SPF. Depending on which UV filters are used, it can be tricky to get a good balance of UV protection. Something that is also challenging is to create a product that still gives effect after swimming or exercising, i.e. that is water-resistant. This is obviously important to the user but can be difficult to achieve without making the product sticky. It is also very important to not use sunscreen sparingly. In order to get the protection promised on the packaging, you must apply it in an even layer and reapply at regular intervals, especially if you have bathed or exercised. 

UV-INDEX – TELLS US HOW DANGEROUS THE SUN RAYS ARE

The UV index is an international standard used to measure how intense - and thus harmful - UV rays are. With the help of the UV index, we can compare how intense the UV rays are at different places and times. The scale is linear and the higher the index value, the stronger the UV radiation is that you are exposed to. An illustration of the UV index in Figure 1 shows what the UV index normally is like in Sweden.

In Scandinavian countries, the UV index is usually between 4 and 7 during the summer season and lower than or equal to 2 during the winter, which would explain our longing for the sun every spring! At a low UV index, one does not need sunscreen, but at a high UV index, the risks of negative effects from the radiation increase and then you need to protect yourself.  

(This is an example of a typical day at summer in Scandinavian countries) 

HOW DOES SUNSCREEN WORK?

Sunscreen products contain specific ingredients that protect you from UV radiation. Like all cosmetic products, sunscreen products are regulated by authorities, such as the European Commission, FDA (in the USA) or CFDA (in China). These products are only allowed to contain certain substances and in specific quantities. Manufacturing a sunscreen product that meets all the requirements and that also provides full protection as well as feels pleasant on the skin is a complicated and costly process.

There are different types of protective ingredients in sunscreens. These ingredients work by either absorbing or reflecting UV radiation - or a combination of both. In this way, they reduce the amount of harmful UV radiation that penetrates the skin and affects the body's cells. Therefore, the sunscreen filters need to remain on the skin's surface for them to be effective.

When discussing sunscreen filters, we usually divide them into chemical and physical filters. These have different properties and differ in efficiency as well as in how they affect the skin.  

CHEMICAL FILTERS

Most sunscreen ingredients that are available are chemical filters. For them to be effective, they need to be dissolved in oils and fats. Some chemical filters break down in the presence of sunlight. This reduces their sun protection properties. Additionally, in some cases, harmful substances can form, which for instance, can cause allergies or be hormonally disruptive. Chemical filters only have the effect of UV protection when dissolved in other substances such as oils and waxes. The most skin-friendly and effective UV filters have a high molecular weight and a high melting point, which means that they do not penetrate the skin. They also require a lot of oil for them to dissolve in the formulation, which in turn can make the product feel sticky to apply, especially on a hot and sweaty day. 

Now we will deep-dive into the chemical filters. For the consumer, it is difficult to understand which filter that is on the product since most chemical filters have several names. In addition, the use of filters varies in different parts of the world.  Several of the more newly developed chemical UV filters are restricted for use by FDA and that means that the US market uses many filters which are phased out in Europe and most parts of the world, due to safety risks.

UVB BLOCKERS

Aminobenzoates were one of the first UV-filters. They are the most potent UVB absorber but do not absorb UVA. Their use has declined due to para-aminobenzoic acid (PABA) sensitivity. PABA is a very effective UVB filter; however, it was reportedly the most common photoallergen and contact allergen and is now phased out.

Cinnamates have replaced PABA as the next most potent UVB absorber and include octinoxate (Ethylhexyl methoxycinnamate) and cinoxate. Octinoxate is the most commonly used UVB filter in the United States. However, Octinaxate is not very photostable and degrades in the presence of sunlight after a short period of time. Cinnoxate is less commonly used.

Salicylates are weak UVB absorbers and therefore used at higher concentrations. They are also used to increase the effect of other UVB filters. Examples of these are homosalate (Trimethylcyclohexyl salicylate) and octisalate (Ethylhexyl salicylate)

Octocrylene is a very commonly used chemical filter but has recently also been associated with phototoxicity and photoallergic potential.

Ensulizole is a pure UVB filter. It is a water-soluble compound that is commonly used in skincare products that are in need of a lighter, less oily feel. Although reported to cause photoallergy, it is considered as a low-level sensitizer. 

UVA BLOCKERS

Benzophenones absorb mostly UVB; however, oxybenzone is considered a broad spectrum absorber as it can absorb UVA as well. However, out of all the sunscreens, oxybenzone has the greatest likelihood of inducing contact or photo contact dermatitis.

Avobenzones are considered broad-spectrum and have a high efficacy against UVA (>380 nm); however, they are very photounstable.

Ecamsule and Drometrizole trisiloxane 
Ecamsule is made up of terephthalyidene dicamphor sulfonic acid, a very photostable product and seems to stay on top of the skin with limited risk of penetration. Same accounts for Drometrizole trisiloxane. Ecamsule is approved by the FDA. Drometrizole trisiloxane is not yet approved by the FDA. Approved in EU, Canada, Australia, and Japan.

Broad-spectrum sunscreens
Ethylene-bis-benzotriazolyl tetramethylbutylphenol (MBBT) (Tinosorb M) and bis- ethylhexyloxyphenol methoxyphenyl triazine (BEMT) (Tinosorb S) are examples of broad-spectrum filters. Both filters are large molecules which decrease the likelihood of systemic absorption or endocrine effects. They are also considered to be photostable and non-irritating to the skin.

None of these filters are approved by FDA and therefore not available in the US. They are both available in Europe, Australia, and other countries.

Chemical sunscreen (INCI): Benzophenone-3 (Oxybenzone), Octylmethoxycinnamate / Ethylhexyl Methoxycinnamate (Octinoxate), Homosalate Trimethylcyclohexyl salicylate) ), Octyl salicylate/Octisalate (Ethylhexyl salicylate) (), Octocrylene (2-ethylhexyl 2-cyano-3,3-diphenylacrylate), Butyl Methoxydibenzoylmethane (Avobenzone), Bis-Ethylhexyoxyphenol Methoxyphenyl Triazine (Tinosorb S), Drometrizole trisiloxane (Mexoryl XL), Ethylene-bis-benzotriazolyl tetramethylbutylphenol (Tinosorb M), Ecamsule (Mexoryl SX).

PHYSICAL FILTERS

The mechanism of action of physical sunscreen is based on the reflection and scattering of UV light, pretty much in the same way as clothing.

Physical filters are the ones that cover the skin in a white layer. Zinc oxide and titanium dioxide are two filters that are often combined to provide optimum UV protection. Zinc oxide protects against a wide range of UVA and it is very photostable and does not react with other UV filters. It is more effective than titanium dioxide in regards to UVA protection however, it is less efficient against UVB radiation.

Titanium dioxide protects against UVA and UVB, but does not protect against UVA (340 to 400 nm). Both Zinc and Titanium dioxide is very photostable and does not react with other UV filters.

Many consumers dislike the white coating that physical filters leave on the body. As a result, manufacturers have started to produce filters with smaller particles, known as nanoparticles. The smaller the particles, the less of a white layer the filter leaves on the skin. Nanoparticles are still too large to be able to penetrate the skin but can be dangerous if inhaled. Moreover, they can be toxic to corals, fish, and other organisms. Since 2013, it has been mandatory to label products containing nanoparticles in the EU. For instance, a sunscreen might be labeled as follows: Zinc Oxide (Nano).

For many reasons, it is dangerous to inhale nanoparticles, but they do not penetrate the skin. If concerned about the ingestion of nano-particles, my advice would be to either avoid the nanoparticles or use lotions or cremes instead of sunscreen sprays containing the nano-particles.

Basically, physical filters cannot penetrate the skin but remain on the surface of the skin where they can protect against the harmful radiation. Since physical filters cannot penetrate the skin, the body is less likely to react to them than to the chemical filters. It is among other things the low risk of allergies and the lack of hormone-disrupting effects that make physical filters often used for children and for people with sensitive skin.

Physical sunscreen (INCI): Titanium Dioxide, Zinc Oxide

 

Sunscreen

The most common UV filters used in sunscreen products are listed in Table 1.

Table 1. UV filters used in Europe and their limitations. INCI stands for International Nomenclature of Cosmetic Ingredients and is the name listed on the ingredient list. USAN stands for United States Adopted Name and is the name used for American products. 

Sunscreen

HOW TO CHOOSE THE RIGHT SUNSCREEN AND HOW TO USE IT RIGHT

When choosing a sunscreen product there are countless options. To minimize the risks of being in the sun and to reduce the use of sunscreen products, the best way is to get fully dressed and avoid the sun when it is high in the sky. In addition, it is important to regularly apply a product that protects against both UVA and UVB radiation and that is also water-resistant with medium or high protection, depending on where you are. By choosing products that are fragrance-free, you do yourself and your skin a favor because perfumes are among the most allergenic substances used in cosmetic products, an effect that even can be exacerbated by sunlight. To find the right product for you, consider:

  • What skin type you have. Fair and red-headed people need to protect themselves to a greater extent in order not to burn.
  • How bright the sun is. Check how high the UV index is in your area.
  • For sensitive skin, physical filters may be kinder to the skin than chemical filters. They often give a blue and white cast on the skin, which essentially shows where you have applied the product.
  • Make sure your sunscreen gives you proper protection, choose a product with a UVA symbol and that is water-resistant. That way, the protection does not decrease as much when you bath or sweat.
  • It is also important to choose a photo-stable product that does not lose its effect when you stay in the sun.

To get the best sun protection possible, you should use at least as much of the product as the manufacturer recommends, because that is the amount that has been used when testing the product. A person's skin surface is usually estimated to be about two square meters and the amount of product used in the SPF tests is two milligrams per square centimeter. This corresponds to 40 grams, which is more than what most people use when applying sunscreen. A common standard used to get enough cream is to apply a cupped hand amount to the whole body. If you use spray or mousse, it is much more difficult to get an idea of how much is needed, since it is not possible to measure in the same way. In addition, it is best to apply a smaller amount to one body part at a time, to get as smooth and even of an application as possible.

A study has shown that sun protection increases significantly when product is applied several times (Heerfordt, Torsnes, Philipsen, & Wulf, 2018). Also, it is easier to get a better application if you apply sunscreen before you go out in the sun and start sweating. Of course, you also need to be cautious about continuously reapplying sunscreen during the day. How often it is needed depends on how active you are and how much the product rubs off, but it is best to reapply your sunscreen every two hours and after bathing.  

DRESS TO PROTECT

Clothing is the first line of defense against the sun. The right clothes offer more certain sun protection than sunscreen, since people often don’t use sunscreen in the right way (unevenly applied and forget to reapply).

How do different items of clothing affect how well you’re protected? How can you be sure a piece effectively blocks the sun’s rays? 

Here are some tips:

  1. Dark clothing - black and navy blue, absorb more UV rays than lighter colors like whites and pastels. For example, an everyday white cotton T-shirt has an SPF of only about 10. As a rule of thumb, the more intense the hue, the better protection the clothing will provide.

  2. Material: Like color, the material, weave, and texture of your clothing can affect how well it protects you from UV rays. Synthetic and semisynthetic fibers like polyester or rayon are the best choices for sun protection, as are dense, heavy, tightly woven fabrics like wool, denim or corduroy. On the opposite end of the spectrum are lightweight fabrics (for example refined cotton), which tend to be thinner and let more light pass through.
  • Example: Shirt (Denim-jeans) SPF 1700
  • Blouse 100% viscous: SPF:15
  • T-shirt 100% cotton: SPF 10
  1. Size: It’s pretty obvious that the more skin you cover, the better protected you are. It can be easy to forget that the same thing applies to hats! The best hats for sun protection have a wide brim (3-inches or greater). Look for a tightly woven hat, rather than a straw hat that allows UV to pass through its openings. Don’t forget to check the fit of your sunglasses too — a pair that slips down your nose is leaving your eyes at risk for sun damage. Look for sturdy sunglasses with wide lenses that cover the eyes, eyelids and as much of the surrounding areas as possible.
  1. Loose fit: A loose fit shirt is providing better SPF than a tight one.

Sotirios Maipas, Polyxeni Nicolopoulou-Stamati, Sun lotion chemicals as endocrine disruptors, HORMONES 2015, 14(1):32-46.

Krause, A. Klit, M. Blomberg Jensen, T. Søeborg, H. Frederiksen, M. Schlumpf, W. Lichtensteiger, N. E. Skakkebaek, K. T. Drzewiecki. Sunscreens: are they beneficial for health? An overview of endocrine disrupting properties of UV‐filters. International Journal of Andrology, Vol 35, 3:424-436, 2012.

Syed Niaz Ali Shah, Zahir Shah, Muzammal Hussain and Muzaffar Khan. Hazardous Effects of Titanium Dioxide Nanoparticles in Ecosystem. Bioinorg Chem Appl. 2017; 2017: 4101735

Mana Man Na Yung, Catherine Mouneyrac and Kenneth Mei Yee Leung. Ecotoxicity of Zinc Oxide Nanoparticles in the Marine Environment. Encyclopedia of Nanotechnology, Springer Netherlands, Editors: Bharat Bhushan, pp.1-17, 2014.