What is SPF in Sunscreen Lotion?

[simple-author-box] The SPF that we hear about and read on product labels is a measure of the kind of protection you’ll get from UVB rays. These are the harmful rays that can cause skin cancer and give you sunburns.

SPF = Sun Protection Factor

Skin that would normally burn after 10 minutes in the sun can be protected with an SPF sunscreen. Unfortunately, the SPF in lotions can be deceptive.

Most people don’t understand the way it works, and don’t apply it correctly. SPF measures the amount of time you can spend in the sun without getting a sunburn based on how quickly you burn without it.

It’s a tough measure for consumers who are not doctors, and don’t always understand the way sunscreen works. Each SPF number has two values that contribute to its overall effectiveness.

SPF 15

With an SPF of 15, that’s the lowest you can go towards protecting yourself from UVB rays.

If you burn in the sun after 10 minutes, a level of 15 will allow you to stay in the sun 15 times that amount. With that math, you’d have 150 minutes of sun protection.

There’s another factor as well. With an SPF of 15, you’re getting 94% blockage of UVB rays. The sunscreen doesn’t factor in UVA rays in its calculations.

SPF 30

This is the medium amount of coverage that you can get with sunscreen. It’s the one that provides good value for the percentage and SPF, too.

With the formula described above, you’d get 300 minutes of sun protection with this sunscreen. That’s about 5 hours of protection against 97 perfect of UVB rays.

SPF 50

As you reach the higher end of the spectrum for UVB protection, you’re not actually getting more in the way of protection.

It’s 98 percent blockage of UVB rays. The difference between SPF 15 and 50 is only 4%, so people think they are getting more protection with a higher SPF, but the coverage isn’t significantly better.

Measuring UVB Protection

When you buy a sunscreen, you’re getting up to 98 percent skin protection depending on how much you use and how often you reapply.

Unfortunately, the sunscreen doesn’t provide much in the way of UVA protection.

UVA is still a huge problem when it comes to skin cancers and other skin problems like premature aging.

Here’s a helpful video from Howcast on the difference between UVA and UVB rays.

Applying the Right Amount

One of the factors that can reduce the protection provided by sunscreens no matter their SPF is reapplication. Many people get to the beach or out into the sun after applying sunscreen and spend the entire day in the sun without reapplying it.

The lotion can wash away in the ocean, wear away from sweating, or degrade against the punishing rays of the sun. Manufacturers do try to warn consumers about reapply sunscreen every few hours, but many do not.

They’re having fun and forget, or don’t understand how vital reapplication is to remaining sunburn free.

Here’s an informative video on how to apply sunscreen from Dr. Urmila Nischal of Doctor’s Circle.

High SPF Delusions

With a high SPF, users believe they’re more protected against the harmful rays of the sun. In fact, it leads to a false sense of security.

Users assume they can spend the entire day in the sun without worrying that they might burn. After a day in the sun, they’ll return to find they’re sunburned.

It’s a painful lesson in reapplying sunscreen and not believing that you’re fully covered for full skin exposure.

swimming with a burn

The high SPF products might even prevent sunburn, but they aren’t protecting against UVA rays since they have minimal protection against it.

That’s true of every level of SPF, but with higher protection, consumers are likely to engage in riskier behaviors because they think they’re being protected.

The Best Ingredients

Instead of looking at the SPF rating alone, you should be looking at ingredients. The best number for protection is around an SPF of 30.

That will protect you from damaging UVB rays and allow you to stay in the sun for 150 minutes. It’s important to reapply throughout that time, too.

Aside from the SPF, you should be searching for sunscreens with ingredients that will block UVA rays, too. Those are the rays that can cause serious damage as well. There should be some combination of UVA and UVB blocking ingredients.

The best ones are zinc oxide, titanium dioxide, or avobenzone.

If you don’t really want to read ingredients on every label, find ones that are labeled multi-spectrum, UVA/UVB protection, or broad spectrum protection. They’ll have some form of protection for both types of sun rays.

Read our article, What Are The Ingredients in Sunscreen and What Do They Do?


It’s important to seek shade when you become overheated instead of relying on the protection of your sunscreen. Buy the right type of SPF with a broad spectrum protection. Reapply often and liberally.

Most people don’t use enough lotion because they don’t want to spend time rubbing in all that lotion, but it’s vital to protecting your skin over the long term.

About the author: Sariya is our resident tanning expert.  Being Turkish, she has a tendency to tan easily, which she considers a blessing. At the same time, Sariya minored in chemistry, so, when it comes to various lotions and bronzers, Siriya knows a thing or two.  As much as she loves her tan, she knows that sun safety is also very important.