We all have it in our minds that we have to apply sunscreen before stepping out of our homes on a sunny day. We all look for a sunscreen with a higher SPF number written on the packaging. However, do you really know what it means?
The SPF on sunscreen stands for Sun protection Factor. It is a relative measurement for the amount of time that your sunscreen will protect your skin from the harmful ultraviolet rays.
UVB Rays - These rays primarily affect the epidermis which is the outer layer of the skin. This can lead to sunburns and surface level skin cancer.
UVA Rays - The sun also emits UVA rays which affects the dermis which is the lower level of the skin. These rays are typically associated with tanning.
SPF number basically targets the UVB rays. However, some sunscreens can protect against the UVA rays.
Sunscreen SPF And Skin Protection
If your skin normally burns after staying 10 minutes in the sun, then you can go for SPF 15 sunscreen which will allow you to stay for longer in the sun without burning for approximately 150 minutes.
This is just a rough estimate and really depends upon your skin type, intensity of the sunlight and the sunscreen used. SPF is actually a measure of protection from the amount of UVB exposure. Therefore, it is not really meant to help you determine the duration of exposure.
For best protection, experts usually recommend using a minimum SPF 15 sunscreen. Apply it on your skin before stepping out and reapply it after every 2 hours.
SPF 15 - Blocks 93% of UVB Rays
SPF 30 - Blocks 97% Of UVB Rays
SPF 50 - Blocks 98% of UVB rays
SPF 100 - Blocks 99% of UVB rays
So, a way to see this is that SPF 30 sunscreen only gives you 4% more protection than SPF 15 sunscreen. Another way to look at it is:
SPF 15 which gives 93% protection allows 7 out of 100 photons through.
SPF 30 which gives 97% protection allows 3 out of 100 photons through.
So, using an SPF 30 might not double your level of protection but it will block half the radiation that an SPF 15 would let through to your skin.
Why Not Use A Really High SPF Sunscreen?
A sunscreen with higher SPF might give you slightly better protection than a sunscreen with lower SPF. However, the downside is that it gives you a false sense of protection. This way you might spend more time in the sun and increase your risk of sunburn and skin cancer. Therefore, you need to choose your sunscreen carefully.