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All You Need to Know About SPF In 10 Minutes
1.Why is protecting your skin important?

Sunlight is what powers our Earth, however Ultraviolet light (UV) within it can result in skin aging and more importantly can lead to more significant skin diseases which includes skin cancers such as basal cell carcinoma, squamous cell carcinomas and melanoma.


2.What is SPF and what does it do?

SPF stands for “Sun Protection Factor” and is an internationally accepted standard by which the efficacy of sunscreen is assessed. It is based on the ability of a particular sunscreen formula to prevent sunburn which is principally caused by UVB.


3.What is ultraviolet light and why is it bad for you?

Ultraviolet light also known as UV radiation forms part of what is called the electromagnetic spectrum. The electromagnetic spectrum is the term used by scientists to describe the entire range of light that exists which is classified by its wavelength. UV light occupies the spectrum of wavelengths ranging from 10-400nm(see diagram). UV light is divided into 3 different bands: UVA, UVB and UVC. UVC is almost completely filtered out by the ozone layer and therefore does not usually form part of the discussion. It is UVB and UVA that is mainly responsible for damage to the skin. UVB causes direct damage to the DNA of the cells in your skin leading to skin cancer while UVA is thought to exert its effect on your skin via production of free radicals.



4.What does the term “Factor” mean and how do you choose which factor is most appropriate for you?

As discussed above, SPF refers to the ability of a sunscreen to protect against UVB only. The factor level and its relative ability to protect against UVB is show in the diagram below. As can be appreciated from the diagram there isn’t a linear relationship between SPF level and sun protection. 



Once you go beyond SPF 30 the level of protection afforded is not significantly higher. In order to protect against the effects of UVA, you will need to use a “broad spectrum” sunscreen. If you’re considering using a sunscreen my recommendation would be to use a sunscreen that is labelled as “ broad spectrum” with an SPF 50 and above.




However, another technique is to choose an SPF based on your Fitzpatrick skin type as shown in the diagram below.



5.What does PA ++++ mean?

The PA rating is a measure of the effectiveness of the sunscreen in protecting against UVA. The rating system was developed in Japan and was adapted from the Persistent Pigment Darkening (PPD) method. Simply stated, this technique exposes an individual to UVA and assess the extent of their tanning. The greater the UVA exposure required to achieve a specific degree of tanning the higher the PA rating of the sunscreen. So a sunscreen with a PA rating of 10 allows an individual to handle 10 times as much UVA exposure as compared to a sunscreen with a PA rating of 1 (as measured by the Persistent Pigment Darkening method).

 A rough conversion of a products PPD rating to PA rating is as follows:

If a product’s PPD = 2 to 4, PA = PA+
If a product’s PPD = 4 to 8, PA = PA++
If a product’s PPD = 8 to 16, PA = PA+++
If a product’s PPD = 16 or higher, PA = PA++++

PA+ means your sunscreen provides some protection against UVA rays while PA++ provides moderate protection and PA+++ and PA++++ offer even higher degrees of protection being rated amongst the best.


6.Chemical vs mineral sunscreens

Suncreens are divided most commonly into “mineral/physical” sunscreens and “chemical/synthetic” sunscreens. Mineral sunscreen ingredients mainly include zinc oxide and titanium dioxide while chemical sunscreens can include a number of agents the most common of which include oxybenzone, octinoxate, octisalate, and avobenzone. Mineral sunscreens work mainly by deflecting/scattering the suns UV rays while chemical sunscreens undergo disintegration of their ingredients which deactivates UV rays and prevents them from harming the skin. There has been a lot of controversy with regards to which is better but recent improvements in chemical sunscreens have meant that the difference between the two is minimal. Therefore my recommendation when choosing a sunscreen for yourself is that you make it based on what feels better on your skin rather than if its mineral or chemical. If you still want some practical evidence of how effective chemical sunscreens are have a look at this video on Youtube:


7.Perfume/essential oils in sunscreen

Some sunscreens are scented and although I don’t have a huge problem with sunscreen that smells nice, you have to be aware of how you skin reacts to perfume. Individuals with sensitive skin may react to perfume/essential oils in their sunscreen and this reaction maybe made worse by exposure to heat/sunlight.


8.How do you apply it to your skin?

How difficult could this be? This may sound simple and straightforward, you slap it onto sun exposed sites and you’re done right? Well I wish it was as simple as that! One of the major issues with sunscreen application is getting the quantity right. There are a number of studies that have shown that the amount of sunscreen applied is usually inadequate. Liberal application 20 minutes prior exposure is essential followed by regular top-up depending on what activity you’re undertaking. Generally a top up every 2-4 hours is required while if you’re playing sports or swimming topping up much more frequently is recommended.


9.When should you start using sunscreen?

Sunscreen should be used as early as possible in life. There is good evidence that cumulative sun exposure in childhood correlates with increased incidence of melanoma. Sunscreen should also be worn on cloudy days as the sun’s UV rays are still present and even within the home on a sunny day. To further protect against UV rays one can also clothing that has an SPF rating, sit in the shade and avoid going out during the hottest part of the day.


10.Are there any problems associated with the use of sunscreen?

Two commonly encountered areas of controversy with regards to the use of sunscreen include:

  1. Does sunscreen inhibit production of vitamin B?

The simple answer to this question is that although sunscreens may reduce the extent of vitamin D synthesis in your skin when exposed to sunlight, it is unlikely that you will become deficient due to it. This is more common in individuals with inherited disorders   such as xeroderma pigmentosum who undergo strict sun protection measures rather than your average healthy individual. Furthermore, studies have shown that a significant proportion of people are vitamin D deficient whether they use sun protection or not, and require vitamin D supplementation.


  1. Do sunscreen ingredients actually cause more harm to skin than their protective function?

There have been concerns that certain ingredients (especially in chemical sunscreens) may enter the blood stream and have negative consequences on the endocrine system as well as producing free radicals on reaction with UV rays which may then go on to damage your skin. Suffice it to say that the research in this area is quite limited and confined to almost exclusively invitro studies whose conclusions are in most circumstances quite difficult to extrapolate to real life. The benefits of sunscreen have been established beyond any reasonable doubt while the theoretical harms have not yet established any firm basis of evidence despite over 40 years since the invention of sunscreen in the form we know it today.


Further reading:

Haywood R, Wardman P, Sanders R, Linge C. Sunscreens inadequately protect against ultraviolet-A-induced free radicals in skin: implications for skin aging and melanoma?. J Invest Dermatol. 2003;121(4):862‐868. doi:10.1046/j.1523-1747.2003.12498.x


Lim HW, Naylor M, Hönigsmann H, et al. American Academy of Dermatology Consensus Conference on UVA protection of sunscreens: summary and recommendations. Washington, DC, Feb 4, 2000. J Am Acad Dermatol. 2001;44(3):505‐508. doi:10.1067/mjd.2001.112913


What is PA +++


Sorry but Korean sunscreens are better than Western ones


June 08, 2020 — Dr J

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