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Why are SPF and sunscreen so important? Most people don’t apply enough sunscreen which means that they do not receive the level of UV protection stated on the bottle. This is particularly the case when people use “moisturisers with added SPF”. In addition, these moisturisers often contain no UVA protection (A good PA rating).
In order to achieve the UVA and UVB protection values stated on a sunscreen, you need to be using 2mg of sunscreen per cm2 (2mg/cm2). This is because this is the standard amount of sunscreen used to calculate the SPF and UVA-PF values during testing. This translates to around 1.0 – 1.5 grams to cover an adult human face.
This quantity is difficult to visualise, which is why we have shortcuts like the 2 or 3 finger rule, shot glass full, coin-sized dollop, ¼ teaspoon etc. These are good shortcuts that work especially well for chemical sunscreen lotions which have a specific gravity of 1 (1ml = 1gram).
Physical sunscreens (like SPF with Zinc Oxide) tend to be denser – you get more weight per volume; they don’t flow like lotions. So it is difficult to measure them out using these shortcuts. But on the upside, you will get better protection for the same volume of sunscreen!
Your best bet is to rely on a proper method of application rather than worrying about weight or volume measurements. Having a uniform layer of sunscreen on your skin is more important than the total weight of sunscreen you use. Read our blog about effective sunscreen application to know more.