Sun protection factor (SPF) and ultraviolet protection factor (UPF) explained

Curious Chloride’s Sun Protection Guide Part 2.

Staying inside while the sun is shining outside is for most of us, not an alternative. We love summer and sunshine but as we all know; the bright side has a dark side.

Read the second part in our sun-series to get learn how you can enjoy the nice weather – without harming your skin! 


Safe sun time

Apart from seeking shade, the best way to be protected from the sun is to wear clothes. A simple rule comes from The Skin Cancer Foundation,

“The more skin you cover, the better.”

They recommend that optimal clothing in hot sunny weather are

  • long pants
  • wide-brimmed hats
  • long sleeves, preferably tightly woven and (as a suggestion) loose fitting.

This is evidently not how we are used to seeing people on the beach and will for most require some configuration to the normal attire.

According to the Skin Cancer Foundation, it is widely recommended to use protective clothing as a First Line of Defence against the sun’s UV radiation. Sun protection factor (SPF) creams and sprays should only be viewed as a complement to clothing.

Clothing is the “First Line of Defence” against the sun

Using language that makes you associate the sun’s rays with a battlefield might sound too alarmist. But the more you read on the topic, the more it becomes apparent of how much more efficient clothing is compared to sunscreen creams.

A study in the Journal of Clinical Pharmacology and Therapeutics reports that there is also an over-belief in the protection-powers of sunscreens.

”Sunscreens protect against sunburn, but there is no evidence that they protect against basal cell carcinoma or melanoma. Problems lie in the behavior of individuals who use sunscreens to stay out longer in the sun than they otherwise would.

Vitamin D inhibition is, at this stage, unlikely due to insufficient use by individuals. Safety of sunscreens is a concern, and sunscreen companies have emotionally and inaccurately promoted the use of sunscreens.”

How to dress appropriately in the sun. 

Ultraviolet Protection Factor (UPF)

How can I protect my skin from the sun without sunscreen? By using the appropriate UPF clothing.

The Ultraviolet Protection Factor (UPF) measures how much UV radiation is absorbed by fabrics. UPF protects against both UVA and UVB, on the contrary to SPF.

Different fabrics protect differently and as a baseline, the darker and more tightly woven a piece of fabric is, the better the sun protection.

“In general, clothing made of tightly-woven fabric best protects skin from the sun. The easiest way to test if a fabric can protect your skin is to hold it up to the light. If you can see through it, then UV radiation can penetrate it – and your skin.” The Skin Cancer Foundation explains.

UPF sun protection examples:

  • White cotton t-shirt: UPF 7
  • Wet white cotton t-shirt*: UPF 3
  • Green cotton t-shirt: UPF 10
  • Long sleeved dark denim shirt: UPF 1,700
  • Thicker & darker fabric (such as black or blue velvet): UPF 50

*Wet fabrics can lose up to 50 percent of their UPF!

“As a rule, light-colored, lightweight and loosely-woven fabrics do not offer much protection from the sun. That white T-shirt you slip on at the beach when you feel your skin burning provides only moderate protection from sunburn, with an average ultraviolet protection factor (UPF) of 7.

At the other end of the spectrum, a long-sleeved dark denim shirt offers an estimated UPF of 1,700 – which amounts to a complete sunblock.” The Skin Cancer Foundation again.

The face is the most sensitive to the sun’s rays

There is evidence that our face is particularly sensitive to the sun’s rays. And this is because our face rarely is covered in clothing. Clothing that can protect from the sun = decreases the risk of sun damaged skin and skin cancers. (read more about the dangers of UV light here)

One suggestion would be to wear a facekini, which looks unusual but apparently works effectively.

SPF – Sun Protection Factor 

As we all know, we can also protect ourselves from harmful UV rays with different products containing sun protection factor (SPF). SPF is a rating for products containing UVB protection- UVB only!). (Learn the difference of UVB and UVA here)


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How is SPF calculated?

The number following SPF is supposed to tell you for how long you can stay in the sun before getting red or burned.

See the example from the Skin cancer foundation,

“If it takes 20 minutes for your unprotected skin to start turning red, using an SPF 15 sunscreen theoretically prevents reddening 15 times longer — about five hours”

But unfortunately, it is not all that easy. The issue with SPF is that it only protects against UVB rays, so even if you avoid getting red or burned, the “invisible” UVA rays may still damage your skin unnoticeably.

It is therefore very important to find a broad-spectrum sunscreen that protects from both UVA and UVB. This is also important if you work inside by a sunny window, as UVA can affect the skin through the glass.