SPF Explained: What Does SPF Really Mean?

When shopping for sunscreen, it’s easy to be overwhelmed by the array of SPF numbers on every bottle. From SPF 15 to SPF 100, what do these numbers actually mean? Is higher always better? And how does SPF relate to real protection from the sun?

In this guide, we’ll break down what SPF really means, how it works, and how to choose the best SPF level for your skin and lifestyle.

What Does SPF Stand For?

SPF stands for Sun Protection Factor. It measures how well a sunscreen protects your skin from UVB rays—the type of ultraviolet radiation that causes sunburn and contributes to skin cancer.

In simple terms, the SPF number tells you how long you can stay in the sun without burning when using sunscreen correctly, compared to without it.

Example:

If you normally start to burn after 10 minutes in the sun, applying SPF 30 would theoretically allow you to stay in the sun 30 times longer (i.e., 300 minutes) without burning.

How Does SPF Work?

SPF works by blocking or absorbing UVB rays before they penetrate your skin. The higher the SPF number, the greater the level of protection:

• SPF 15 blocks about 93% of UVB rays

• SPF 30 blocks about 97%

• SPF 50 blocks about 98%

• SPF 100 blocks about 99%

While higher SPF offers more protection, no sunscreen blocks 100% of UV rays. Plus, the difference in protection between SPF 30 and SPF 50 is marginal—just 1%.

SPF Only Covers UVB, Not UVA

It’s important to note that SPF only measures UVB protection. It does not indicate protection against UVA rays, which penetrate deeper into the skin and contribute to premature aging and skin cancer.

To get complete protection, look for a broad-spectrum sunscreen, which shields you from both UVA and UVB rays.

SPF Numbers: What’s Right for You?

Choosing the right SPF depends on your skin type, how long you’ll be outside, and the intensity of the sun in your location.

General Recommendations:

• SPF 15: Good for everyday, limited sun exposure (e.g., walking the dog)

• SPF 30: Great for daily use and moderate outdoor activities

• SPF 50+: Ideal for extended sun exposure, fair skin, or at the beach or pool

If you burn easily or have very fair skin, go for SPF 50 or higher. For darker skin tones, SPF 30 is generally sufficient, but daily use is still essential for protection against UV damage and discoloration.

Application Matters More Than the Number

Even the best SPF won’t work if not applied correctly. Most people apply only 25–50% of the recommended amount of sunscreen, reducing its effectiveness significantly.

Tips for Proper SPF Application:

• Use about 1 ounce (a shot glass full) to cover your entire body

• Apply sunscreen 15–30 minutes before going outdoors

• Reapply every 2 hours, or immediately after swimming or sweating

• Don’t forget easy-to-miss areas like ears, neck, tops of feet, and scalp

SPF in Makeup and Moisturizers—Is It Enough?

While it’s great that many makeup products and moisturizers include SPF, they shouldn’t be your only source of sun protection. The amount applied is usually too small to provide full coverage.

If you’re relying on SPF in your foundation, make sure to layer it over a dedicated sunscreen for full protection.

SPF Myths You Should Stop Believing

Myth 1: Higher SPF means you don’t need to reapply.
Truth: All SPF needs reapplication every 2 hours.

Myth 2: Darker skin doesn’t need sunscreen.
Truth: Everyone, regardless of skin tone, needs sun protection.

Myth 3: You don’t need sunscreen on cloudy days.
Truth: Up to 80% of UV rays can penetrate clouds.

Final Thoughts

Understanding what SPF really means empowers you to make smarter skincare choices. It’s not just about picking the highest number on the shelf—it’s about applying the right SPF correctly and consistently.

For most people, SPF 30 or 50 with broad-spectrum protection is the sweet spot. Combine it with sun-safe habits like wearing hats, sunglasses, and staying in the shade for all-day protection.