How Much More Protection Do Higher SPF Sunscreens Really Provide?

Our trips will take you to places where the sun can be unrelenting.  If you're going to Galapagos and mainland Ecuador, or the Okavango Delta and the Kalahari desert, or even to polar regions the highly reflective snow and ice, you absolutely need to consider protecting your skin from the sun's powerful rays - more so if you're leaving home during your winter season and your skin has not been exposed to the sun for months.  

We typically suggest that the best way to protect your skin is to keep the sun from shining on it in the first place. Long sleeves, long pants, a wide-brimmed hat.  But that's not always fun - it's nice to feel a warm tropical breeze on your skin after having been cooped up in cold climates for months! And even with a wide-brimmed hat, UV radiation is reflected onto your face by water surfaces, ice, snow and sand.  

An effective sunscreen is therefore a critical component of your packing list.  There is a lot of gobbledygook on sunscreens out there in the social media world.  We thought we'd help you cut through the nonsense with the following article (thanks to ChatGPT for the help...).  

 

How high should the SPF rating be?

At a glance, sunscreen labels biggest a simple equation: higher SPF equals significantly better protection. In reality, the relationship between Sun Protection Factor (SPF) and ultraviolet (UVB) protection is nonlinear, with diminishing incremental gains as SPF increases.

What SPF actually measures
SPF refers specifically to protection against UVB radiation—the primary cause of sunburn and a contributor to skin cancer. An SPF rating indicates how much longer skin can theoretically be exposed to UVB before burning, compared to unprotected skin. More precisely, it reflects the proportion of UVB radiation blocked.

The nonlinear protection curve
The key insight is that SPF gains flatten out at higher levels:

• SPF 15 blocks about 93% of UVB rays

• SPF 30 blocks about 97%

• SPF 50 blocks about 98%

• SPF 100 blocks about 99%

The jump from SPF 15 to SPF 30 reduces UVB penetration by roughly half (from 7% to 3%). But moving from SPF 30 to SPF 50 only reduces it from 3% to 2%. In absolute terms, that’s just a 1 percentage point improvement.

 

 

Why the small differences could matter
Although the incremental gains appear modest, they are not trivial—especially over prolonged exposure. The difference between 2% and 3% UVB transmission represents a 33% relative reduction in UV exposure, which can be meaningful for individuals at higher risk (e.g., fair skin, history of skin cancer, or intense equatorial sun).

Real-world performance considerations
Laboratory SPF values assume ideal conditions: generous application (2 mg/cm²) and even coverage. In practice, most people apply far less, effectively reducing the achieved SPF—often by half or more. Under-application makes higher-SPF products a useful buffer against imperfect use.

Beyond SPF: broad-spectrum protection
SPF does not measure protection against UVA radiation, which penetrates deeper into the skin and contributes to aging and cancer risk. A “broad-spectrum” sunscreen—covering both UVA and UVB—is therefore more important than chasing very high SPF numbers alone.  Thankfully, in many jurisdictions (including the U.S. and Canada), sunscreens must meet regulatory criteria to be labeled “broad spectrum” and most reputable sunscreens on shelves today clearly state “broad spectrum” or “UVA/UVB protection” on the packaging.

Bottom line
Increasing SPF does improve UVB protection, but with sharply diminishing returns beyond SPF 30. For most users, consistent application of a broad-spectrum SPF 30–50 sunscreen, reapplied appropriately, offers a well-balanced and effective level of protection. Higher SPF products provide marginal but sometimes meaningful additional protection—particularly as a safeguard against under-application.

 

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