As we approach spring and begin to worry about sun exposure, I find that many people are confused by all the various abbreviations you hear around sunscreens. So let’s take a moment and understand what they mean.
The A band is that part of ultraviolet that is the longest wavelength (UVA). This is the part of the ultraviolet spectrum that has the least amount of energy. It makes up for it by going deeper into the skin. It normally does not cause burns but it will make your skin look older because it is damaging to the deeper structures of your skin.
UVA is found year round and all day. Though it is not as strong as UVB, there is more of it and its effects are cumulative. It will cause cancer.
The B band (UVB) is the shorter wavelength. It has more energy than UVA but does not penetrate as deep. Because it is much higher energy, it easily causes skin burns. It is more likely to cause cancer because it has more energy but less likely to cause age damage because it does not penetrate very deep. UVB is normally found in the late Spring, Summer, and early Fall. It peaks as the sun gets high overhead and is gone by 4 pm.
SPF stands for sun protection factor. This is the number that is used to measure sunscreen protection and is given as a number. Examples include SPF 15, SPF 30, and SPF 50.
To understand what SPF means, you have to know how it is measured. The most common way to measure SPF is to start with a volunteer. A fixed amount of sunscreen is put on their skin and they are exposed to ultraviolet light to see how long it takes for their skin to turn red. This is compared to how long it takes for their skin to turn red without the sunscreen. The difference in time is the SPF.
There are a few things that are important to understand:
- SPF is measured by how long it takes to lightly burn the skin. UVA does not burn the skin. SPF DOES NOT MEASURE UVA ACTIVITY. It is important to realize that all those sunscreens with SPF measurements are not measuring the UVA protection; the wavelength that makes your skin look older.
- SPF is measured in very controlled situations using using artificial sunlight. The measurement does not take into account all the variability that can occur. So even though an SPF 15 should provide 15 times longer protection, the results are never that good. This is a little like EPA mileage estimates which are always a little higher than you actually get. So when using sunscreens for UVB protection, it is better to use a higher SPF that feels good than a lower one.
- Higher SPF sunscreens get that rating by being thicker. These tend to be less comfortable on your skin than sunscreens with lower SPF. High quality sunscreens are usually more comfortable on your skin for a given SPF.
- Most sunscreens breakdown when exposed to sunlight. This means that as you wear them, they are becoming less effective and the SPF factor is going down. This is why you need to reapply sunscreens and another reason why it helps to wear a larger SPF factor.
- Just to repeat, SPF does not measureUVA protection. If you want UVA protection (to keep you skin looking younger) then you need to use a UVA protecting sunscreen. Just remember there are no measurements for UVA.
Beside putting sunscreen on your skin, you can protect yourself by wearing clothing. But how much protection does clothing give you? For the longest time, clothing manufacturers tried to use SPF to estimate how well a particular clothing item would protect you from the sun. In 1998 the UPF scale was launched as a new way to test clothing. Clothes are tested under laboratory conditions which determine how well the clothing protects from sun exposure.
A UPF of 30 is not the same as an SPF of 30. UPF 30 means that because of the material, the weave, and several other factors, that only 1 photon (particle of ultraviolet light energy) will pass through the clothing out of 30. For a UPF of 40 this means 1 in 40. UPF protection does not go higher than 50+.
It is important to understand that you can’t always tell how well a fabric will block out UV light by looking at how much regular light gets through. You can only tell by looking at the tag which will show the UPF rating if it has been tested. The following table explains the quality of the protection:
|UPF Rating||Protection Category||% UV radiation Blocked|
|UPF 15 – 24||Good||93.3 – 95.9|
|UPF 25 – 39||Very Good||96.0 – 97.4|
|UPF 40 – 50+||Excellent||97.5 – 99+|