general sensitive skin

Chemical vs Physical and How to Choose the Best Sunscreen



This resource aims to cover a lot of ground on how the sun affects the skin. We use scientific, peer reviewed literature wherever possible to support our findings. It’s our hope that the content of this article sheds some light (pun intended) on common misconceptions around sun exposure, skin health, and sun protection.

What’s the Danger of Sun Exposure for Our Skin?

While our favourite star gives us a lot of fairly useful benefits - generally warming our planet, enabling photosynthesis, and providing the foundational requirements for all living things - it comes with some inherent dangers, especially for our skin.

These dangers include UV rays. There are three types: UVC, UVB, and UVA. They differ in their length of their waves, biological activity (AKA how significantly they affect living cells), and the depth to which they can penetrate the skin. Generally speaking, shorter wavelengths are more harmful despite penetrating the skin less deeply 1. UVC rays are the shortest wavelengths emitted by the sun. They’re extremely biologically active and very dangerous to humans but thanks to our trusty ozone layer, they’re completely filtered out by the atmosphere.

Medium-wavelength UVB-rays are also very biologically active. They’re responsible for sun burns and the delayed tanning effect that we enjoy after a visit to the beach. These rays cannot penetrate beyond the superficial skin layers 2 and most are filtered by the atmosphere. They can’t pass through glass, clothing, or clouds but don’t take them lightly, UVB rays have been attributed to some of the most common forms of skin cancer.

UVA rays are relatively long form radiation. They penetrate deeper into the skin, can pass through glass and some clothing, and they account for about 95% of the sun's radiation 3UVA rays cause the immediate tanning effect while also contributing to most visible signs of skin aging including wrinkling, elastosis, actinic keratoses, irregular pigmentation, and telangiectases (AKA spider veins) 4It has been reported that as much as 90% of visible skin aging is caused by the sun’s radiation; the majority of this damage comes from UVA rays 5Previously, it was thought that UVA could not cause any lasting damage. Recent studies strongly suggest that it may also enhance the development of skin cancers 6.

As a consumer it’s important to understand that the Sun Protection Factor (SPF) is ONLY a measure of protection against UVB rays. In technical terms SPF is a ratio between the time it takes for reddening or sunburn to start in skin protected with sunscreen compared with unprotected skin under the same conditions. For example, if it takes 20 minutes without protection to produce reddening or sunburn, an SPF 15 sunscreen might prevent reddening 15 times longer — about five hours 7. Sadly, this is a theoretical ratio and in real-life we can’t just take the SPF number as a measure of “time protected”. Lots of factors can impact how long you’ll be protected with sunscreen, such as hair colour, skin tone, hydration, previous sun exposure, and eye colour 8. The right combination of these factors can reduce your five-hour window from the calculation above into a much more dangerous 30 minutes!

With this understanding of the SPF number, it goes without saying that SPF isn’t a percentage of protection. This comes as a surprise to many but according to the Canadian Cancer Society, a rating of SPF 15 means the product is tested to block 93 per cent of UVB rays; an SPF 30 blocks 97 per cent. And those crazy, SPF 110 sunscreens? Well they only block about 98.9per cent of UVB rays9. As you can see there is a diminishing return on real protection as SPF levels increase. Health Canada and the FDA recognize this diminishing return and its potential to mislead consumers. As a result, they recently capped the maximum SPF level for new sunscreens at 50. If a sunscreen has a sun protection factor beyond 50, it must be labelled as SPF 50+10.

As we’ve discussed in this article, it’s not only the UVB radiation that our skin needs protection from. Both UVB and UVA exposure can have serious implications for our health. This makes it imperative that we choose a sunscreen which protects us from both. But, how do we know?

How to Choose a sunscreen

When you’re looking at sun protection options, there is no shortage of products to chose from. To start with, you should select a sunscreen with sufficient SPF. As we’ve discussed above, the right SPF for your skin is a bit of a moving target. As a rule of thumb, many dermatologists recommend selecting sunscreens with an SPF of 30 or higher for daily use and 50 or so for a day at the beach. Of course, if you are fair skinned, have red hair, freckles, or light coloured eyes, you may want to opt for a higher SPF sunscreen in daily use.

Always look for “broad spectrum” sunscreens. This term is intended to describe products that offer protection against both UVA and UVB rays. Unfortunately, there is no rating system for UVA protection that is equivalent to the UVB-focused SPF system in Canada. So in many cases the term “broad spectrum” can be a bit of a misnomer. To help clarify, Health Canada has recently adopted use the UVA protection logo already used in Europe11. 

This simple symbol indicates that a sunscreen producer has used considerable UVA protecting ingredients in their sunscreen. It is a regulated symbol meaning that only qualifying sunscreens are permitted to use it. Make sure you see this when you are making your next sunscreen purchase.

What are my Options?

There has been a lot of recent discussion about the different types of sunscreens available: Which is best, which is safer, etc.  And while manufacturers are getting more and more creative with their labelling, the surprising truth is that there are only really two types of sunscreens: Chemical, and physical.

These two categories of are based on the active ingredients (or sun filters) used in each. Chemical sunscreens use human-made sun filters which act by absorbing UV energy like a sponge and converting it to heat that is then dispersed in the skin12. This category of sunscreens are also referred to as “organic” or “synthetic”. Their active ingredients have long, anxiety inducing names like “octocrylene”, and “oxybenzone” but don’t let that scare you. These chemicals are very effective at protecting our skin from UV radiation. They have been thoroughly studied and deemed safe and effective by Health Canada and the US Food & Drug Administration. Generally, in instances where individuals have reactions to sunscreens e.g. in 2017 where Banana Boat products seemed to be literally burning the skin on toddler’s faces, it is usually the result of other ingredients and / or the combination of ingredients in the formulation which are to blame, not the sun filters themselves.

The second category of sunscreens, commonly referred to as “physical”, work by reflecting UV rays, bouncing them away from the skin 13. These sunscreens have a few commonly used synonyms including “inorganic”, “mineral”, and “natural”. However, the last of which is a bit of a misnomer. While physical sunscreens use zinc and titanium as their active ingredients - naturally derived minerals found in the earth - these ingredients are intensely processed before they can be used in a sunscreen. In the case of water resistant "natural" sunscreens, each mineral molecule must be coated with chemical layers of polymer or silica to ensure it remains on the skin after swimming or sweating 14, 15. Often a “natural” sunscreen has gone through almost as much processing as any chemical alternative. 

While there are only two categories of sunscreens there are no shortage of synonyms. The table below shows the synonyms used to refer to each.

Chemical Sunscreen

AKA Synthetic

AKA Organic

AKA by their filters. The presence of any one of the below filters means the sunscreen at least in some part a member of this category:

Physical Sunscreen

AKA Natural

AKA Inorganic

AKA Mineral

AKA by their filters. The presence of any one of the below filters means the sunscreen at least in some part a member of this category:


Physical (natural) sunscreens vs. Chemical sunscreens

Cosmetic Appearance and Usability

One of the most common complaints a dermatologist will hear regarding physical a sunscreen is its opaqueness. While modern physical sunscreens have come a long way, physical sunscreens from years past would typically leave a chalky, white residue on the face.  This occurs because the sun filter particles that protect our skin in physical sunscreens (zinc and titanium) are traditionally quite large in size. These particles are what you see when you notice an ashy, grey film left on the skin 16.

Some recent developments have significantly improved the wearability of physical sunscreens as manufacturers work to decrease the size of sun filter particles while maintaining the same level of UV protection. The most effective development in this realm has been the integration of nano-particles into sunscreen. Nano-particles are tiny, around 15nm (that's 0.0000015 millimeters or 15 billionths of a meter). Using particles this size significantly increases the spreadability and transparency of sunscreen formulations. It helps to prevent that opaque, ashy residue that plagued physical sunscreens for so long. Studies have also found that reducing sun filter particles to nano-size can help improve their protective ability as they can better disperse UV radiation 17.

In North America, nanoparticles are a relatively new feature in sunscreens as for years they were widely misunderstood. At one time, it was believed that these particles were so small they would be transferred into our blood through the skin and accumulate in our bodies to poison us. While that certainly sounds concerning, the notion has been widely disproven through various studies in the early 2000’s which found that nano-sized sun filters could not permeate the skin in any significant quantity 18, 19.Like many cosmetic ingredients, the only danger that these particles pose to human health is in the manufacturing process where they could be inhaled if airborne and the correct personal protective equipment is not worn 20

In terms of usability, physical sunscreens have a major advantage over chemical sunscreens: They take affect right away. Physical sunscreens don’t require time to absorb before they become effective. This is due to their mechanism of protection, they sit on the surface of our skin and reflect UV radiation. On the other hand, chemical sunscreens require time to bind to the skin before they become effective 21. This usually takes around 20-30 minutes.

Protective ability

Until the 1990s the commercially available chemical sunscreens were only effective against UVB radiation. This meant that the UVA radiation which causes visible signs of aging and some forms of skin cancer was still getting through to our skin. The introduction of a chemical filter called Avobenzone changed this by offering protection into the UVA spectrum for chemical sunscreens. While avobenzone still offers the best UVA protection available in the USA it has one major flaw: Photostability. On its own, Avobenzone loses its effectiveness by 50% every half-hour that it is exposed to sunlight. It requires other UV filters such as octocrylene and/or oxybenzone to stabilize it 22

This creates a significant advantage for physical sun filters which offer broad spectrum protection (covering UVA and UVB), with increased photostability 23.

Tolerance for Sensitive Skin

For individuals with sensitive skin, physical sun filters cause lower allergenicity and sensitization which means less skin irritation than chemical UV filters 24, 25. This point makes physical sun filters a great candidate in children’s sun protection. Furthermore, on absorbing the UV photons, chemical UV filters can release free-radicals and consequently cause damage to collagen, elastin or skin cell DNA 26. However, the degree to which this damage occurs requires further study.

Will sunscreen stop me from getting the Vitamin D that I need?

At one time, it was thought that the use of sunscreen would reduce vitamin D production in our bodies to an insufficient level. The idea was that as vitamin D requires UV radiation to activate, we wouldn’t have enough vitamin D if we were using sunscreen to block all of the UV radiation from our skin. Recent studies have proven this to be untrue. Using multiple subjects, these studies found that despite our best efforts, when we apply sunscreen we don’t cover single square centimeter of our skin. What’s more, we often don’t use enough. Most consumers only apply between 25% and 50% of the recommended 30ml of sunscreen per whole-body application 27.  As consumers, in our daily use of sunscreen we inevitably leave some areas unprotected, or thinly protected and available for vitamin D activation. Further, it’s important to remember that sunscreens don’t block all UV radiation. Even SPF 50 only blocks 99% of UV radiation, letting some through to help our bodies produce much needed vitamin D 28.

Water Resistant vs. Water Proof Sunscreens and How to Interpret their Labels

While there is no such thing as a water proof sunscreen, there are two terms that you will see relating to water resistance on sunscreen products:

  • Water Resistant (effective for up to 40 minutes in water)
  • Very Water Resistant (effective for up to 80 minutes in water)

According to Health Canada and the FDA, these are the only legal ways that a sunscreen producer can talk about the water resistance of a new sunscreen. Essentially, they are telling us that the sunscreen provides protection while swimming or sweating up to the time listed on the label. Similarly, products may carry a "sweat resistant" or "very sweat resistant" claim if the parameters for "water resistance" or "very water resistant" testing (respectively) have been met 29.

Sunscreen manufacturers now are banned from claiming that a sunscreen is "waterproof" or "sweat proof," as Health Canada and the FDA have determined that those terms are misleading.

Even when using a water-resistant sunscreen, you should reapply after getting out of the water or after sweating.

Sunscreen Vs Sunblock

Historically, the word sunscreen was used for products that contain chemical ingredients that absorb and breakdown UV rays, while “sunblock” was used for those with natural, mineral filters like zinc or titanium. However, the new rules from Health Canada have ruled the term “sunblock” to be misleading and it can no longer be used. The term sunscreen is now used generically for all types of sun protection 30.


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  18. ALLEN, N.S.; EDGE, M.; ORTEGA, A.; LIAUWA, C.M.; STRATTONB, J.; MCINTYRE, R.B. Behaviour of nanoparticle (ultrafine) titanium dioxide pigments and stabilisers on the photooxidative stability of water based acrylic and isocyanate based acrylic coatings. Polym. Degrad. Stab., v.78, n.3, p.467-478, 2002.
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