Dermatology

What SPF Should You Use? Here’s What Dermatologists Recommend

Now that summer is here, you and your family may be preparing to spend some time outdoors in the sunshine. As you pack the essentials, don’t forget sunscreen! But will just any kind of sunscreen work? And what kind of SPF should you use?

Florida Medical Clinic dermatologist and Mohs surgeon J. Kevin Poitras, MD, is here to help you understand SPF and how choosing the right sunscreen can help shield you from sun damage. That way, you can safely prepare for your next picnic or beach trip.

What does “SPF” stand for?

SPF stands for sun protection factor. A sunscreen’s SPF is a relative measure of how well it protects your skin from the damage caused by UVB rays.

What do SPF numbers mean?

An SPF of 30 means that it takes 30 times as long to produce a slight redness in your skin (called erythema) when using the sunscreen than it would take without sunscreen.  So, if it takes your skin 10 minutes to develop a slight redness without sunscreen, it would take 5 hours to develop the same amount of redness with an SPF 30 sunscreen.

However, it’s important to note that SPF is measured in a laboratory under very controlled conditions, and often using a very narrow portion of the UV spectrum. When you’re outside, many other factors come into play, such as sweating, water reflection, and even where you’re located on Earth.

You can think of SPF values like the EPA fuel efficiency ratings found on new automobile sales sheets. They both frequently overrate their effectiveness, but are still very useful for comparing one product to another.

Sunscreen doesn’t start working instantly, either. It can take up to 30 minutes for your skin to fully absorb it. For better protection, sunscreen should be applied indoors 20 to 30 minutes before going outside.

Does a higher SPF mean a sunscreen is more effective?

Not necessarily. While sunscreen with a higher SPF technically blocks out more UV rays, there are diminishing returns as the number climbs. There’s a big difference between SPF 10 and SPF 20 — but not as big of a difference between SPF 30 and SPF 60.

Also, a higher SPF does NOT mean that it needs to be applied less frequently. Not all high SPF sunscreens offer broad-spectrum protection, either. 

When possible, go with a broad-spectrum sunscreen of at least 30 SPF.

 To be clear, an SPF higher than 30 isn’t harmful or ineffective. If you have SPF 50, use and reapply it as often as you would SPF 30.

You should also know that when we talk about SPF, we’re only talking about protection from a specific type of UV radiation: UVB rays. Let’s learn a little more about the three types of UV rays and how they affect us. 

Types of UV Rays 

There are three types of UV radiation: UVA, UVB, and UVC rays. While they all come from the sun, only UVA and UVB rays reach the Earth’s surface.

  • UVA: The vast majority (95%) of UV rays that reach the Earth’s surface are UVA rays. In addition to being active in cancer production, they play a major role in the skin’s aging process and the formation of wrinkles.
  • UVB: UVB rays account for the other 5% of UV light that reaches us from the sun. These are considered the most deadly. UVB rays damage the skin’s DNA and are the primary cause of skin reddening, sunburn, and skin cancer.
  • UVC: Because they’re absorbed by the Earth’s ozone, UVC rays never reach the surface. However, you can still find man-made UVC rays in some tanning beds, welding torches, and welding lamps.

Damage from UV Rays

Both UVA and UVB radiation can damage your skin in the short-term (by causing painful sunburns) and in the long-term (by causing skin cancer). These rays can also lead to aging changes, such as thinning of the skin and wrinkles.  

It’s important to understand that even brief exposure to UV light will damage skin cells. This damage can occur directly to the cells’ DNA, or indirectly by the production of substances which may then damage DNA.

An infographic showing the effect of sunscreen in blocking UV rays

The Importance of Broad-Spectrum Protection

You don’t have to get a sunburn for damage to occur.  

Although UVB rays are blocked by window glass, UVA rays are not. That means even when you’re inside, you are exposed to some UV radiation. This is one reason current studies suggest that the best protection comes from daily use of sunscreen to the most exposed areas on the body.

Because SPF only measures effectiveness against UVB rays, it shouldn’t be the only thing you look for on a sunscreen label. Unfortunately, there isn’t a simple system like SPF to indicate the degree of UVA protection. So, to shield yourself against UVA rays, it’s important to choose a sunscreen labeled for “broad-spectrum” protection.

Natural Skin Pigmentation and Sun Protection

Our skin contains cells called melanocytes. These cells produce a group of substances called melanins, which give us some degree of natural protection against some of the damage done by UV light.

People with darker complexions produce more melanin, which gives them more natural protection. However, this is NOT complete protection. Skin cancers do occur, although with less frequency, in people with darker skin. 

The SPF factor of melanin is not as high as some people might think. Laboratory measurements suggest that black skin has an effective SPF of about 13. That means the lower prevalence of skin cancers in people with darker skin may be partly due to the fact that, despite the low SPF of melanin, they are “wearing” their sunscreen all the time.

No matter your skin color, daily sunscreen application is still important, especially to areas such as the face, neck, arms and hands, which have the highest incidences of skin cancer.

A cloudy day at the beach

Do you have to wear sunscreen when it’s cloudy outside?

Yes. It’s important to wear sunscreen even if it’s cloudy during the day and you can’t see the sun.

The sun radiates different types of rays. Visible rays are just one type—the sun also emits UVA and UVB rays, which are invisible to the naked eye. UVA and UVB rays are harmful and can pass through clouds.

Infrared rays, which the skin senses as heat, are absorbed by the water in clouds. That means that on cloudy days you may not feel the sun’s heat, but you’re being exposed to UV rays. You still need sunscreen to protect you, even when it’s not sunny or hot.

What’s the difference between physical and chemical sunscreen? 

Different sunscreen ingredients have different ways of protecting your skin. A sunscreen may be categorized as a physical or chemical protectant depending on how it interacts with UV rays.

A physical sunscreen sits on the top layer of your skin instead of being absorbed. The ingredients reflect rays from the sun. Physical sunscreen is gentle on the skin, but is easily shed when sweating and may leave a white sheen when applied. Ingredients usually include zinc oxide or titanium dioxide.

A chemical sunscreen absorbs into your skin. It works by absorbing UV rays and then releasing them as heat. People with sensitive skin may find that chemical sunscreen can sting or cause irritation. However, chemical sunscreens are water-resistant, so they’re useful if you’re sweating a lot or going for a swim. Ingredients usually include oxybenzone or avobenzone. 

Both types are suitable for decreasing your risk of sun damage—as long as you choose a product that has at least 30 SPF and is labeled broad-spectrum.

Other Ways to Stay Protected From the Sun

Even though wearing a 30 SPF sunscreen is important, sunscreen alone is not enough to prevent skin damage. You should still protect yourself in other ways when possible. Other ways you can reduce your risk include: 

  • Wearing a hat or visor
  • Wearing long sleeves or pants
  • Staying in the shade when possible
  • Limiting your time outside when UV light from the sun is at its peak (typically 11am to 4pm)
  • Going inside if your skin feels like its burning or turning red

Don’t forget to reapply sunscreen immediately after swimming, sweating, or after 2 hours of direct sun exposure. You won’t always be able to predict when and how long you’ll be outdoors, so it’s also a good idea to carry a travel-sized sunscreen with you wherever you go.

Practice Sun Safety Year-Round

Staying protected from the sun is incredibly important. Even if it seems to be an inconvenience  or hassle, applying sunscreen is critical in keeping your skin healthy and preventing cancer. Remember, the sun damages your skin over the course of your entire life, not just when you get a sunburn at the beach.

Florida Medical Clinic has a large team of medical professionals to provide you with treatment for the entire spectrum of skin diseases and cosmetic enhancements. If you already have a biopsy proven skin cancer, don’t delay treatment. Contact the office of Dr. J. Kevin Poitras, MD for more information regarding Mohs surgery and other options.

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Dermatology

About this author.

Dermatology

J. Kevin Poitras, MD

Mohs Micrographic Surgery

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