What does SPF Really Mean Anyway?

Because Dr. Curt Samlaska lives and works in the Henderson and Las Vegas areas, he is familiar with the hot climate and year-round sunny days. He offers advice about Sun Protection Factors (SPF) for people who live and visit the area and spend time outdoors.

Dr. Samlaska says that there are a lot of simple things people can do—the first of which is to avoid peak sunshine times of 11 am to 4 pm during the summer months. These times in the sun can be deadly—this is when people collect a lot of their most intense exposure on their skin.

There are simple things to do to avoid extreme sun exposure: For example, if anyone has access to a pool and it’s shaded in the afternoon but not in the morning, swim in the afternoon—not in the morning. Any amount of shade is going to be helpful.

Use of sunscreen is really important and it works very well, but people don’t realize that they have to reapply it. The American Academy of Dermatology recommends that if anyone is going to be outside all day, sunscreen should be applied every two hours. Most people don’t do that, and that’s one reason why they fail in general.

Dr. Samlaska said that if you’re getting tan, you’re getting damaged. Tanning is a general defense mechanism. If you’re doing the right things, you can be out in the sun and not get tanned. That’s the key.

In addition to being reapplied every two hours, sunscreens are designed to be applied much thicker than most people do. If a sunscreen has an SPF of 30 and it’s put on the arm very thinly, it becomes an SPF of 1 or 2.

SPF stands for Sun Protection Factor—let’s say a certain skin type allows someone to go outside for one hour before they start to get pink. That’s called their minimal erythema dose, which is the amount of radiation skin can take before it gets to its minimal erythema dose.

So if that person with an MED of one hour puts on an SPF of 30 they could be out for 30 straight hours before they received the same amount of radiation dose.

So if they put an SPF of 100 on, they could be outdoors in the sun for 100 hours.

Doesn’t work? Why doesn’t it work? It’s because of how the sunscreen is applied. It’s not put on thick enough—the way it’s designed to be used. Studies show a bottle of sunscreen is only three applications. Who does that?  Not many people. Also, if a person is going to be out for an extended period, they need to reapply every two hours to maintain protection.