Safer Sun (II)
Part II: SPF, UVA and UVB - the ideal factor for your skin
By Dr. Huong Nguyen | Editor: Dr. Sabine Nunius | June 30, 2022
At first glance, it seems quite simple: open the tube, apply sunscreen, reapply frequently to maintain sun protection – done! But not all sunscreens are created equal.
In detail, five key figures are important:
• Skin’s own protection time
• planned duration of sun exposure
• SPF
• UVA
• UVB
UVA AND UVB RADIATION
Ideally, a product should protect you from both UVA and UVB rays. UVB rays only penetrate the epidermis. However, in high doses, they cause the well-known sunburn. In the worst case, they can cause chronic damage to cell nuclei and thus skin cancer. UVA rays have longer wavelengths than UVB radiation and penetrate deep into the dermis. While they don't cause sunburn, they can lead to skin changes such as wrinkles, loss of elasticity, and uneven pigmentation. Regular and adequate protection is therefore important.
THE SUN PROTECTION FACTOR
This number indicates the protection a sunscreen provides against UVB rays—the rays that cause sunburn—but not against UVA rays! It tells you how long your skin's natural protection can be extended by using the sunscreen before sunburn occurs.
For example, your skin has a natural protection time of 20 minutes and you use a sunscreen with SPF 10. In this case, 20 x 10 = 200. This means your skin would be protected by the product for a maximum of 200 minutes.
1. Fact of the day
A sun protection factor (SPF) of 2 absorbs 50 percent of UVB radiation, SPF 20 absorbs 96 percent, and SPF 40 absorbs approximately 98 percent. Sun protection does not increase steadily with the factor; rather, the increase curve becomes increasingly flatter. It never reaches 100 percent.
Of course, to calculate this, you first need to know your skin's correct self-protection time. Ideally, you should have your dermatologist determine this based on your skin type. This table from the Federal Office for Radiation Protection can also help you get an initial orientation:
https://www.bfs.de/DE/themen/opt/uv/wirkung/hauttypen/hauttypen.html
Depending on the skin type, the following self-protection times result:
Phototype
Self-protection time (min)*
Celtic type (Type I)
under 10
Nordic type (Type II)
10 to 20
Mixed type (Type III)
20 to 30
Mediterranean type (Type IV)
over 30
Dark skin types (Type V)
over 60
Black skin types (Type VI)
over 90
*) Self-protection time: maximum time spent in the midday summer sun until erythema (= sunburn) appears
2. Fact of the day
The SPF of a sunscreen refers only to its UVB protection. You can tell whether a sunscreen product also offers UVA protection by the 'UVA in a circle' pictogram on the packaging. The corresponding UVA protection is then at least one-third of the UVB protection.
After this little math introduction for everyday life, it's now time to learn how to use it correctly. Simply click on to the next Safer Sun story!
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