Safer Sun (III)
Part III: More is better? The right amount of sunscreen
By Dr. Huong Nguyen | Editor: Dr. Sabine Nunius | June 30, 2022
MORE HELPS MUCH?
You know what SPF you need—so its use is now self-explanatory!? Not quite, because there's a little plot twist.
To achieve the SPF declared on the packaging, an application rate of 2 mg/cm2 is required. So, you'll need to apply the cream very generously!
To illustrate:
• You need about two finger lengths (= the length of your index and middle fingers) of cream for your face and décolleté alone. These are actually finger lengths, not widths.
• For an adult's entire body, you'll need about 30 to 40 ml, or about a fifth of a 200 ml bottle! A ten-year-old child needs about 20 ml of sunscreen.
If you're wondering when the last time you used so much cream was, you're not alone!
Fact of the day
To achieve the SPF declared on the packaging, you would need an application amount of 2 mg/cm2!
Actual sun protection effect is overestimated
Experts estimate that in practice, only one-third of the stated sun protection factor is actually achieved. This generally overestimates the protective effect. Anyone who applies a sunscreen with SPF 50 but only half the required amount doesn't get SPF 25 – as you might expect. The protective effect doesn't decrease linearly, but exponentially: The square root of 50 results in an SPF of approximately 7. And that's actually too low!
However, this isn't primarily our fault, but rather the fact that we need to apply a VERY thick layer of product to achieve the specified SPF. I often find it difficult to adhere to the recommended amounts, especially when applying the almost obligatory sunscreen every day after my facial moisturizer.
WHAT TO DO?
So how do we get out of this dilemma? We can simply get into the habit of shortening our time in the sun and not fully utilizing the calculated, individual protection time! Some official sources even recommend, as a rule of thumb, only using up to about a quarter of the maximum exposure time. This way, we can avoid sunburn and also minimize the risk of long-term effects caused by light.
WHY CAN'T WE EXTEND OUR STAY DEFEATING AFTER APPLYING CREAM?
Despite sunscreen, a certain dose of radiation reaches the skin per unit of time. This accumulates over the course of a day until the skin's tolerance limit is reached. This exposure can only be used once per day, otherwise the skin's repair mechanisms will be overloaded. Repeated application does not extend this time. However, by regularly reapplying sunscreen, we ensure that the sun protection film on the skin, which develops holes due to sweating, bathing, or abrasion (when drying), is refilled.
WHEN TO APPLY CREAM?
It's often said that sunscreen should be applied 20 to 30 minutes before sun exposure. This rule is a thing of the past. Both sunscreens with chemical UV filters and sunscreens with mineral filters (such as titanium oxide or zinc oxide) are sufficient if they are applied to the skin shortly before first sun exposure. However, it always takes a while in the sun before we are fully covered in sunscreen. Therefore, it is actually advisable to start sunbathing "prepared" and in full sun protection gear.
WHAT'S NEXT?
We're almost at the end of our Safer Sun series. Finally, we'll cover two more topics in this series :
• Which UV filters should I use?
• How can I strengthen my UV defense through diet?
We look forward to seeing you again!
Until then, safe sunscreening!