Sunlight damages your skin, even if you have dark skin or a dark tan. If you are going to be out in the sun, you need to protect yourself with sun block that counters the damaging rays of the sun.

What Does SPF Mean with Sun Block?

Skin cancer is by far the most common form of cancer suffered by people. This is maddening to many medical professionals because preventing skin cancer is not only possible, it is simple. When you are going to be outside for a significant amount of time, you should wear sun screen or sun block. For those of us who don’t have nearly as much hair as we used to and would like to have, a hat is advisable as well.

As you might know, not all sun protection is created equally. There are a number of factors that go into how much protection it provides you. The first is time. If the block is only good for one hour, you need to re-apply it accordingly. The second factor is the SPF of the product in question.

So, what is SPF? SPF stands for Sun Protection Factor. You might have been expecting something more scientific, but there you are. SPF comes in different levels designated by a numeric system. Generally, anything under SPF 15 isn’t really worth buying because it provides minimal protection at best. SPF of 15 up through the high twenties provides a better shield against the damaging rays of the sun, but still lets a certain amount of penetration. SPF 30 or above offers the best sun protection.

On the technical side of things, SPF is not just a random number assigned by the producers of sun screen. The number actually represents a measurement of time, although loosely so in my opinion. The measure of time is determined by calculating how long you can stay out in the sun without any protection before getting a sun burn. The SPF designation is then a multiple of that time if you were the sun protection product. Let’s look at an example.

Assume you can stay out in the sun for 10 minutes before getting sunburned if you wear no protection. A sunscreen with a SPF 20 rating would then be representing that you could stay out in the sun for a 200 minutes or twenty times the period without sun protection.

As you probably noticed, there are a few problems with this calculation. First, you don’t know how long it takes for your skin to get burned and probably don’t want to find out. Second, the calculation assumes you don’t go in the water or lose coverage because of sweat. This is why it is best to reapply sun block every couple of hours or immediately after going in the water despite what the product may represent regarding being waterproof.

In general, it is best to use sun protection with a minimum of a SPF 15 rating. It is also advisable to apply it liberally and often. Doing so can prevent you from seeing your skin age quickly, not to mention preventing skin cancer.

John Grimes is with All Terrain - makers of natural sun protection products for the outdoors.