Home Skin Care Sun protection factor: effect and calculation

Sun protection factor: effect and calculation

by Josephine Andrews
Published: Last Updated on 224 views

The sun protection factor of a sunscreen indicates by which factor the individual self-protection of the skin is extended. The skin type and the intensity of the sun’s rays play a role in this. Read here what you should consider when choosing the sun protection factor and how you can optimize your sun protection.

What does “sun protection factor” mean?

One of the most important information on a pack of sun milk or sun cream is the sun protection factor. It is abbreviated as SPF and is a measure of the effectiveness of sunscreen products. The term sun protection factor is used in the English version as “sun protection factor”, abbreviated SPF.

Sun protection with a high sun protection factor ensures a high level of protection against UVB rays. Otherwise, these penetrate into the upper skin layer and burn and inflame the skin cells – sunburn occurs. UV radiation also increases the risk of skin cancer.

The light protection classes

To make it easier to use and understand the sun protection factors, they are divided into four classes. For example, you can quickly access the product you need when you are abroad. In Europe, the protection classes mean the following:

SPF six and ten: light protection (low)
SPF 15, 20 and 25: Medium protection (medium)
SPF 30 and 50: high protection (high)
LSF 50 plus: very high protection (very high)

Calculate light protection

So that you don’t get sunburnt, you can use the sun protection factor to calculate how long you can spend in the sun each day. To do this, multiply the sun protection factor by your skin ‘s own protection time . This is the length of time that you can be in the sun without sunscreen without damaging your skin. It depends on your own skin type .

A person with skin type II, for example, has a self-protection time of around 10 to 20 minutes. With a sunscreen with sun protection factor 20, this would theoretically mean staying in the sun for 200 to 400 minutes (i.e. about three to seven hours).

However, the Federal Office for Radiation Protection advises that you should only use 60 percent of the calculated protection period for staying in the sun. Because even with sun protection factor 50 or sun protection factor 100, some residual UV radiation penetrates the skin. And even this residue damages the skin permanently and can cause cancer.

Which sun protection factor is the right one?

In spring, when you can finally get out in the fresh air again, you should use at least sunscreen with a sun protection factor of 15. During the winter, the skin is only slightly exposed to the sun’s rays. It is therefore important that you slowly get your skin used to the sun again. This gives the skin enough time to build up its own natural protection.

Different outdoor activities also influence the choice of the right sun protection factor. For example, when gardening for one to two hours, it is advisable to apply an SPF 30. On the other hand, SPF 50 is always recommended for longer bike tours, mountaineering and water sports. Anyone who sweats or has contact with water should choose waterproof product variants.

Also important: UVA and infrared filters

The sun protection factor allows a statement to be made about the UVB protection offered by a sunscreen. Protection from other types of radiation is also important.

UVA protection

UVA light causes the skin to age prematurely – the skin becomes wrinkled and saggy faster, and the pores enlarge. Pigment spots and red veins can also appear. To ensure that your skin ages as slowly as possible, you should definitely ensure that your sunscreen has sufficient UVA protection.

There is a European seal for UVA protection: the abbreviation UVA in a circle. If a product bears this label, then the UVA protection meets the requirements of the European cosmetics association “Cosmetics Europe”. This expert panel requires that the UVA protection factor is at least one third of the sun protection factor. Only then does a sunscreen have the required broad spectrum protection.

Infrared protection

As has been known for some time, in addition to UV rays, other components of sunlight can also prematurely age human skin. The first cosmetics manufacturers have reacted to these research results: They offer sunscreens with infrared protection. This is often based on a complex of antioxidants. These are substances that defuse cell-damaging “free radicals”. The term refers to aggressive chemical compounds that are formed in the skin under the influence of sunlight, among other things.

However, there are still no uniform standards for infrared filters in sunscreens (in contrast to the sun protection factor). Research on this has only just begun.

This is the best way to protect yourself from the sun!

Premature skin aging, genetic damage and skin cancer – the consequences can be so drastic if you do not protect your skin adequately from the sun.

The general rule is: Stay in direct sunlight as little as possible. You should particularly avoid the midday sun between 11 a.m. and 3 p.m., because this is the time when the sun’s rays are most intense in Central Europe. If you like to do sports outside, the morning and evening hours are also better suited for it in terms of circulation.

But don’t forget one thing when you’re enjoying the sun from the shade: you can still get up to 50 percent of the UV light even under a parasol or a dense treetop. You should also apply lotion in the shade!

Incidentally, pre-tanning in the solarium is not good for skin health and is also not suitable as preparatory sun protection before a beach vacation.

We give you an overview of the best ways to protect yourself from the sun.


Sunscreens, when used correctly, can block a large part of the harmful rays from the skin. They are usually available in the form of sprays, creams or milk. Chemical substances in the products filter the radiation. There are currently two types of filters:

Organic UV filters

The natural skin pigment melanin absorbs UV radiation and converts it into heat. Organic UV filters also absorb harmful light in this way: benzophenones, for example, intercept UV-A light and cinnamates filter UV-B light. But there are also substances that filter both UV-A and UV-B rays, so-called broadband filters.

Organic UV filters therefore offer chemical light protection. They dissolve well in sunscreen and form an invisible protective film on the skin. So that the entire UV spectrum is covered, the manufacturers combine various organic components, often together with mineral filters.

Mineral UV filters

Titanium dioxide and zinc oxide are the most important micro-pigments that act as physical sunscreens to protect against UV light . They reflect and scatter light. If you use creams that contain purely mineral filters, the skin looks as if it has been rubbed with chalk.

In order for this white effect to be as small as possible, the manufacturers have reduced the particle size to nanometers. Extensive studies have shown that the nano UV filters titanium dioxide and zinc oxide are harmless in cosmetics. The Federal Institute for Risk Assessment also agrees.

Antioxidants in sunscreen

Sunlight sets off chemical reactions in the skin that cause free radicals. These are harsh chemical molecules that destroy connective tissue and damage both skin cells and their DNA. Therefore, the skin itself uses antioxidants from fruits and vegetables to render the free radicals harmless.

To support this protection, manufacturers also enrich sunscreens with antioxidants such as vitamin E , vitamin B3, coenzyme Q10 or carotenoids. They prevent premature skin aging and are helpful if UV radiation penetrates the skin despite sunscreen.

Tips for the right sunscreen

When buying a suitable sunscreen, pay attention to the following properties:

  • Broad spectrum protection against UV-B and UV-A light
  • Sweat and water resistance
  • good adhesion to the skin
  • Stability to light, air and heat
  • good tolerance even with allergies
  • good shelf life: like most cosmetics, sunscreen has a shelf life of 30 months or has a specified best-before date

This is how you cream yourself properly

In order for your sunscreen to work properly, you should consider the following things:

  • For the first time of the day, apply sunscreen about 30 minutes before sun exposure.
  • Use 40 milliliters for the entire body: A standard pack of 200 milliliters should be empty after the fifth application.
  • Also apply sufficient cream to the so-called sun terraces such as the auricles, nose, lips, décolleté and the backs of hands and feet.
  • Reapply sunscreen to your skin at least every two hours, and definitely after bathing or sweating profusely.
  • Even with lotion on, you should stay in the shade during lunchtime.
  • When sunbathing, remember that you cannot stay in the sun indefinitely, even if you wear sunscreen.
  • Note that the sun protection is not extended by repeated application of the cream.
  • Choose a product with an appropriate sun protection factor.


Experts such as the Federal Office for Radiation Protection and the German Cancer Society generally recommend covering as much body surface as possible with clothing. This is how you protect yourself effectively against premature skin aging and skin cancer. Many manufacturers now specify the UV protection factor of a piece of clothing, especially sportswear. A value of 20 and higher protects you well.

The best sun protection for the scalp and neck is a wide-brimmed hat. It prevents skin damage and sunstroke and should also be worn when bathing if possible.

Speaking of bathing: the water does not completely shield you from UV light. Up to half a meter below the water surface, 60 percent of the sun’s rays still penetrate. Sun creams are often not sufficiently waterproof. More reliable will help special UV protective clothing for bathing. This is particularly suitable for children and people with very light skin.


The eyes are just as vulnerable as the skin. UV light damages both the retina and the cornea of ​​the eye. In addition, it permanently clouds the lens and, in the long term, cataracts develop.

Sunglasses are therefore highly recommended when you are outside in the sun. The best models are those that also cover the sides of the eyes well. When buying, pay attention to the manufacturer’s information “100% UV protection” or “UV 400”.

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