Is SPF 60 twice as good as SPF 30? What is SPF anyway?

SPF stands for Sun Protection Factor, and it measures the level of protection that a sunscreen offers against the sun's harmful ultraviolet (UV) rays. The higher the SPF number, the more protection the sunscreen provides.... kind of....

It is important to note that SPF is a logarithmic scale, which means that the level of protection does not increase linearly with the SPF number. Since this is not a math lesson, lets look at a few examples instead. For example, an SPF 15 sunscreen filters out about 93% of UVB rays, while an SPF 30 sunscreen filters out about 97% of UVB rays. Or said another way, Going from SPF 15 to SPF 30 increases the protection by only 4%.

Here are some examples of the level of protection provided by different SPF numbers:

SPF 15: This sunscreen filters out about 93% of UVB rays. It is a good option for everyday use and is suitable for people who spend limited time in the sun.
SPF 30: This sunscreen filters out about 97% of UVB rays. It is a good choice for people who spend more time in the sun, such as those who work outdoors or participate in outdoor activities.
SPF 60: This sunscreen filters out about 98% of UVB rays, while SPF 90 filters out about 98.9% of UVB rays. They sound impressive... but practically speaking they are about the same as SPF 30.

It is important to remember that no sunscreen provides 100% protection against the sun's rays, and it is still possible to get sunburned even when wearing sunscreen. To achieve the listed SPF values, it is also critical to use the sunscreen correctly. Typically 1oz (or a shot glass full) of sunscreen is needed for a full body. Most sunscreen is sold in 4oz bottles, and it is recommended to re-apply sunscreen every 2 hours. A typical family of 4 at the beach should anticipate going through a few bottles of sunscreen on their trip. In reality - a single bottle will likely last that family multiple outings. This is one of many reasons why protective clothing, such as hats, sunglasses and long-sleeved shirts, and avoiding too much time in the sun, especially during peak hours (10am-4pm) may be even more important than the SPF # on your bottle.

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