What is SPF

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I love the feeling of sunlight touching my skin – especially in spring after a long and cold winter. Nevertheless, you shouldn’t underestimate the power of the UV rays! It’s important for you to first understand what UV light is and why we need to protect ourselves from it. After that is clear, we can go over to the SPF. In this post, I will also explain the different claims on sunscreen products and what you should look out for when you buy a product.

What is UV Light?

The UV light is a part of the sunlight and is invisible to our eyes. There are three different parts of UV light, differentiated by their wavelengths: UVA, UVB and UVC. Let’s have a closer look together at those three and why each of them is important to know.

What is UVA?

UVA rays account for the biggest amount of rays from the sunlight but are less intense than UVB rays. UVA rays can penetrate into deeper skin tissue layer because of their shorter wavelength and are responsible for skin ageing and DNA alteration. With the newest results of research, it is concluded that UVA rays can cause skin cancer as well. UVA rays can penetrate clouds and glass and have the same intensity through all the daylight hours of a day. It is very important for you to understand this about UVA – you are not easily protected from this one, so be aware!

What is UVB?

UVB rays can’t penetrate into deeper skin tissue but do their harm in the outer skin layer (epidermis). They are responsible for sunburn and for skin cancer but also for tanning and photoaging. UVB rays are strongest at lunchtime (11 am to 3 pm), which is why we should stay out of the sun during that period of the day. UVB rays can’t penetrate glass but are more dangerous in higher altitudes or when reflected by surrounding surfaces like snow or sand. This means to be especially aware of UVB rays when you are in the sunlight and even more so when it is at lunchtime or in a bright environment (snow & sand).

What is UVC?

This is the most dangerous type of UV ray. Luckily the ozone layer protects us from UVC rays, through absorbing them.

What is SPF?

The letters SPF stand for “Sun Protection Factor”. This factor describes the approximate additional amount of time you will be protected from UVB rays (only). I am for example a Fitzpatrick Skin Type II which is rather fair. My natural sun skin protection is about 10 minutes. This means that after being in the sunlight for 10 minutes without protection, I will start to get a sunburn. An SPF of 30 for me brings prolonged protection of 300 minutes.

You can calculate your protection time easily yourself with this formula natural protection time * SPF of product = time protected from UVB rays.

Even though your protection time is, in theory, prolonged to sometimes almost infinite time, sunscreen has to be reapplied throughout the day. Why is that? Well, it’s several factors playing together. If we look at our skin it looks rather smooth, right? In reality, our skin has it’s own uneven structure with higher and lower areas (insert pic/graphic). When you apply a sunscreen (or any other cream as a matter of fact) you will always have more product in the very small natural creases and less product on the higher, more exposed parts of the skin.  Sunscreen works best when it is applied as evenly as possible. This means that the higher and lower parts of our skin should be covered with sunscreen. For this, you must apply quite an amount of sunscreen. Experts suggest about 2 tablespoons of sunscreen for full body protection. What also minimizes the protection is, when sunscreen is “taken” off the skin through e. g. rubbing with a towel, water, scratching, the straps of a backpack… So you see that even though our skin is protected in theory for a long time when sunscreen is applied properly, it’s still safer to reapply every 2-3 hours.

UVA Star Rating

The UVA Star Rating was developed by Boots in 1992 because until then, there was no indication of UVA ray protection factor. The UVA-protecting factor is measured in-vitro, which means, that it is not measured on human skin (unlike SPF measurements). After the measurement a ratio between UVA: UVB protection is calculated. Because of this ratio, a product can gain 0 – 5 UVA stars. Let’s clarify a bit what exactly I mean with “ratio”. If you have to sunscreens, one with SPF 10 and 5 UVA Stars and one with SPF 50 UVA Stars, which one has the better UVA protection? Exactly, the one with SPF 50! In order to get the best UVA protection Boots to suggest to buy only products with a rating of 4 – 5 stars. And as we have just seen with our little brain gym, the higher SPF you have combined with high UVA Star Rating, the better your broadspectrum/multispectrum protection is and this is what you should be looking for!


The European Cosmetic and Perfumery Association (Colipa) states, that sunscreen is eligible to the claim “waterproof/water-resistant” when the product still offers protection for further 40 minutes after we went into the water.  If the product offers protection for another 60 minutes after swimming, it is allowed to carry the claim “extra water-resistant”. Nevertheless, if you towel-dry yourself, remember that you are rubbing off half the sunscreen as well! Its always safer to reapply sunscreen after swimming.

Basically, it is always better to protect your skin from direct and strong sunlight through clothes or staying in the shade!




By |2019-01-28T14:26:25+00:00January 13th, 2019|Cosmetology|0 Comments

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