Understanding protection for Sun Awareness Week and Skin Cancer Awareness Month

Broad spectrum sunscreen, SPF, PPD and more. What is the best sunscreen?


Taking a stroll, driving in your car or swimming on holiday. Sun exposure can rarely be avoided sometimes. We know that UVA and UVB can be dangerous and may be linked with health complications. We also know that excessive exposure may lead to sunburn and thus damage DNA in skin cells [1]

On a less grim note, we can also protect ourselves from these mean UV rays! There is new research which places emphasis on the importance of UVA protection. But what exactly is UVA, uva sunscreen and how can you protect yourself from it? How is UVA measured or rated? do you need uva and uvb protection?


UVA and UVB rays are the largest contributors to skin cancer and skin ageing. UVA rays are less associated with skin cancer than UVB, though stil definetly play a role and are the number 1 contributor to sun-induced premature ageing. These UVA rays make up the majority of the UV radiation and penetrate deeper into the skin than UVB does[2]. The damage inflicted by the UVA rays is, short term, invisible to the naked eye and is accumulative.

On the other hand, we have UVB rays. These account for about 5% of the UV radiation. They are directly absorbed by DNA as well as melanin which can lead to genetic mutations and if the natural defenses of our cells do not correct it, it can cause skin cancer. The damage due to UVB rays can be immediately visible as sunburn.

Both UVB and UVA levels change depending on the time of day and season. It is apparent that UVA’s penetrative power raises some concerns. It penetrates through glass, for example the side windows of the car, which makes it almost inescapable.

If at this point you are thinking “I do not go to the beach much or tan anyway”, you are wrong. The sun knows no exceptions! It has been estimated that 8% of UVA damage is due to the everyday exposure to the sun such as by walking, sitting near windows etc. Therefore, it is important to know the ratings and measurements you see on the bottle when buying sunscreen, to know how much you are protected and from what.


SPF AKA sun protection factor, is a universal measurement of protection against UVB rays. The number after it is called a multiplier so for example SPF15, which shows how much longer it takes to get a sunburn, in this case it takes 15 times longer(that is assuming you applied the correct amount)!

How SPF is measured is as follows: sunscreen is applied on a person (in vivo) to see how long it takes for their skin to become mildly red. There are also in vitro tests which do not require human test subjects. However, here is the catch. Everyone has a different tolerance for UVB rays, some turn into a tomato within a minute – and some just simply don’t burn.


Persistent pigment darkening is a method of measuring UVA protection that’s similar to SPF. The sunscreen is applied to humans (in vivo) and then expose them to UV light to measure how long it takes for the skin to tan. Like the familiar SPF, the number indicates how long it takes your skin to tan, measuring the strength of the UVA protection.

Boots star rating

This rating is based on the % of the UVA that is absorbed in comparison to the UVB rays. Simply put, it measures how even the UV protection is. These specific tests are done via in vitro tests using machines. If the UVA/UVB ration is close to 1, this means that the sunscreen gets more stars.   

Broad spectrum

Broad spectrum is a term used in most countries to indicate to what extent the sunscreen provides uva and uvb protection. Therefore, uva and uvb sunblock in one. There are a few methods to measure the broad spectrum namely, critical wavelength method and the UVAPF-to-SPF ratio.

Critical Wavelength

In this test, The UV absorbance of a sunscreen is tested (over the entire spectrum;290 – 400nm) and the area under the curve is calculated. The greater the ‘breadth’ of the curve, the broader the spectrum of the protection from the sun.[3] Sunscreens that have a critical wavelength of over 370nm are considered to provide great UVA protection by the FDA.

UVAPF-to-SPF Ratio

The second way of measurement in the broad-spectrum category is the UVAPF-SPF ratio. Though it is a mouthful, it is relatively easy to understand. The UVA protection of a sunscreen must at least be 1/3 of the labelled SPF value. This is done by using special plastic plates or on humans that volunteer. When you see the ratio and the SPF label is high, this means it will provide you with better uva protection sunscreen.

In short, the critical wavelength tells you to what extent the protection of the sunscreen extends, it does not indicate how evenly the protection is spread out. The critical Wavelength test is thus an easier criteria to satisfy. In the US only the critical wavelength is required, whereas in EU and Australia both Critical Wavelength and UVAPF-to-SPF ration is required.[4] In Europe, if both criteria have been satisfied, then the product will have the symbol of UVA in a circle on the packaging.   

What is the best sunscreen?

So now we have a bit more knowledge on what ratings and measurements are shown on our sunscreens. On the other hand, perhaps this was too much information to take in. So to simplify, what is the best sunscreen to use?

In general, it is advised to use broad spectrum sunscreen as this type of sunscreen protects you from both UVA and UVB rays. This means that you have more broad protection, as UVA can cause ageing and UVB can cause sunburn, it takes both into account. This type of sunscreen thus helps to prevent skin cancer and early skin ageing.[5] These type of sunscreens also do not necessarily have to be expensive to be effective.

That is exactly our aim at Altruist. We make broad spectrum uva uvb sunscreen, to not only spread awareness about skin cancer through education, but by also lowering the costs of sunscreen to make it accessible for everyone. If you need a boots 5 star rating sunscreen (since now you know what that means), try Altruist! Not only is it broad spectrum, it is also made for sensitive skin and fragrance and paraben free, for all of you that have a delicate nose!

[1] Moozhipurath, R. K., Kraft, L., & Skiera, B. (2020). Evidence of protective role of Ultraviolet-B (UVB) radiation in reducing COVID-19 deaths. Scientific reports, 10(1), 1-10.

[2] https://labmuffin.com/fact-check-feature-why-you-should-protect-yourself-from-uva/?msclkid=6baf02bcb42511eca02ec5eba5056282

[3] https://drdembny.com/critical-wavelength-and-broad-spectrum-uv-protection/

[4] https://labmuffin.com/fact-check-feature-why-you-should-protect-yourself-from-uva/?msclkid=6baf02bcb42511eca02ec5eba5056282

[5] https://www.aad.org/public/everyday-care/sun-protection/sunscreen/understand-sunscreen-labels#:~:text=Why%20you%20want%20broad%20spectrum,%2C%20wrinkles%2C%20and%20sagging%20skin)