How to choose your sunscreen

How to choose your sunscreen – The point of view of a stem cell researcher

How to choose your sunscreen

Bonjour everyone, 

Today’s article is on “How to choose your sunscreen?”.  This blog post is the foundation of future-review of sunscreens. I share with you my sunscreen requirements that are science-based. What I mean by science is peer-reviewed articles written by researchers. The purpose of applying sunscreens daily is to minimize the negative impact of UV irradiation in your skin cells.  I don’t want you to be just protected. I want you to have the best protection possible to give your skin the best chances to aged gracefully. Whatever your skin color is, you should apply sunscreen every single day. I have diligently applied sunscreen on a daily basis for more than 15 years. 

I will compose a full article on the disastrous effects of the ultraviolet (UV) on the skin. Ultraviolet irradiation is an absolute nightmare for the skin. The worst part is that we do not “feel” their destructive effects unless you have a sunburn. Every single day, rays of sunlight hit the skin and cells are suffering and aging. The fewer UV radiations your skin receive, the better. Hence the daily application of sunscreen but finding a “good” sunscreen is a difficult quest. 

On planet earth, two types of UV are dangerous for the skin UVA and UVB. UVAs are the most vicious because they penetrate deep into the skin while UVB roast the first layers of skin cells in your epidermis and provoke sunburn. 

UVB sun protection factor (SPF): 

The UVB sun protection factor is determined using a standardized in vivo methods. This method assesses the level of protection of a sunscreen against UVB and gives an SPF (Sun Protection Factor) with a number. In many countries (Europe and Australia for example), SPF50+ is indicated when the SPF exceed 60. The SPF translates the time required to get a sunburn.  It means that even with SPF50+ UVB pass through the sunscreen and burn the skin. 

UVA sun protection factor:

The UVAs are likely the one that do the most damage in aging the skin. They are present all year long, even on cloudy day. Unfortunately, there is not a worldwide norma to indicate the UVA sun protection factor on a package. 

Europe UVA factor requirement:

In Europe, the UVA factor has to be a minimum of a third of the SPF (using the persistent pigment darkening (PPD) method). 

It translates as a sunscreen of SPF30 has to obtain a UVA factor of a minimum of 10 (with the PPD method). On the package, a UVA symbol with a circle is indicated. 

Therefore, the protection against UVA increases with the SPF in Europe. Higher SPF equals higher UVA protection.

Japan UVA factor:

Another method is the PA method originally developed by Japan. The level of protection against UVA is translated in  PA associated with +. A PA+ corresponds to 2-4 PPD, PA++ to 4-8, PA+++ 8-15 and PA++++ 16 or above. 

Both European country and Japan use the PPD method to evaluate the UVA protection factor. However, it is not required to have an increase of the UVA protection factor with the SPF. 

First requirement broad spectrum filters:

Sunscreen has to be broad spectrum filtering UVB, UVA I and UVA II. Not all sunscreens protect against the full spectrum of UV lights. 

Second requirement highest UVA and UVB sun protection factor:  

Reason 1:

Higher SPF goes with higher UVA protection (in most cases).

In Europe by the law, the UVA sun factor will increase with the SPF. If the sunscreen uses the PA rating always opt for PA++++. If you buy a European SPF50+ you will have a UVA sun protection factor of 20 or above.  The higher the SPF is, the higher the UVA protection is. This statement is always right in Europe. 

Reason 2:

How to choose your sunscreen second requirement

It has been demonstrated that SPF decrease of 30% after 8 hours of application (in typical day conditions: no water, no sweat, no sport). If you work in an office, stay at home, wear makeup..  you won’t reapply sunscreen every 2 hours (even though we all should).

Conclusion: The higher the SPF is, the higher it will be 8 hours later. 

Nothing is published on the decrease of the UVA protection factor likely it is the same. 

Reason 3:

No sun protection factor is perfect. There is always UVs that path through. The less, the better. The difference of UVB transmission between an SPF30 and SPF50 is only 1%. This 1% seems little but not the SPF result. An SPF of 50 protects your skin 50 times longer than an SPF30. Keep in mind that SPF measures the time to get a sunburn. Even with SPF50 you get a sunburn, it just takes longer.  

Reason 4:

We don’t apply enough. 

See this video from Dr. Dray where she shows how much sunscreen you should apply to have the correct SPF and UVA protection. It is difficult to meet the required dose especially if you wear makeup. Likely, when you use a sunscreen with an SPF50 you get an SPF30. By choosing the highest protection, you have better insurance. 


Third requirement no Alcohol:

Reason 1:


How to choose your sunscreen alcohol

Alcohol or ethanol is a tricky ingredient. As little as 20% to pure ethanol kills cells. I know it for a fact as I use it in my laboratory (I am a stem cell researcher). It creates little holes in the cell membranes and thus killing them. If your skin barrier is damaged or sensitize (by peeling, retinol, vitamin C) ethanol can further inflame the skin. 

Reason 2:

Alcohol is drying and disrupt the composition of our skin lipids. Ethanol as the ability to solubilize lipids making our skin more permeable and dryer.

Reason 3:

Sunscreens are made to be reapplied. Imagine what you do to your skin when you reapply two to three times your sunscreen per day containing alcohol… 

This being said, all I mentioned above is depending on the concentration of ethanol. Ethanol is volatile and evaporates quickly. Its effect depends on its concentration. If your skin is healthy, you can use a sunscreen containing a maximum of 10% of ethanol. I will avoid it if you have hypersensitive skin, skin allergies, rosacea, acne, eczema…  


Fourth requirement safe sunscreen filters: 

This is a complicated matter. Some sunscreen filters are suspected to have an endocrine effect but no in vivo experiment support this claim. The set up of the experiments showing endocrine effects is far from reality. The only consistent data is on the absorption by the skin of Octinoxate (octyl methoxycinnamate or Ethylhexyl Methoxycinnamate). Octinoxate penetrates the skin and is detected in the blood and urine. However, no endocrine effects were detected. The data on the endocrine effects of sunscreen filters are so far insufficient. However, the allergenic and irritant effects of some sunscreen are well documented. Octocrylene is well known to trigger allergies and I do avoid it. 

Based on the scientific literature, the main issue with organic sunscreen filters is their potential allergenic and irritant effects on the skin.  

See down below the list of filters I approved. If you have hyper-sensitive skin opt for mineral-based sunscreens that are primarily Zinc oxide based (Zinc oxide has to appear before titanium dioxide in the formula). I will review organic sunscreens that are compatible with sensitive skin, but you will have to test them on your skin. Nobody can guarantee that you will not develop an allergy.   

Fith requirement nice finish and great under makeup! 

I am pretty sure you have come across with gloopy, tacky, greasy … sunscreens that disturb makeup. Finding, a high broad-spectrum sunscreen with a nice finish and work great under makeup is a quest. 

I have reviewed the Airy UV essence from Klairs (click me for the review). This one is the best I know of as makeup based and for daily used.  I will have for you more reviews on sunscreen with a sunscreen guide. 


My approved sunscreen filters: 

Organic filters: 

  • Tinosorb S: bis-ethylhexyloxyphenol methoxyphenyl triazine, bemotrizinol ⎪(UVA and UVB filter)
  • Tinosorb M: methylene bis-benzotriazolyl tetramethylbutylphenol, bisoctrizole ⎪(UVA and UVB filter)
  • Mexoryl SX: terephthalylidene dicamphor sulfonic acid, Ecamsule ⎪(mainly UVA filter)
  • Uvinul A plus: Diethylamino hydroxybenzoyl hexyl benzoate⎪(UVA)
  • Uvinul T150: Ethylhexyl Triazone⎪(UVB)

Mineral sunscreen 

  • Zinc oxide ⎪(UVA and UVB filter)
  • Titanium dioxide ⎪(UVA and manly UVB filter)



Thank you for reading me. 

A bientôt, 


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