What Does the Number Next to SPF Mean: Should You Choose 15, 30, 50 or 100?

June 2, 2025

When you pick up a sunscreen, the first thing that catches your eye is the number next to the word SPF. SPF 15, 30, 50, 100... What does it mean? Does a higher number always mean better protection? And which SPF is right for you? Let’s break it down — in simple terms, without unnecessary jargon.

SPF: What Is It, Really?

SPF stands for Sun Protection Factor. It indicates how effectively the product blocks UVB rays — the kind responsible for sunburn and, over time, can contribute to skin cancer.

In theory: if your skin starts to redden after 10 minutes in the sun, SPF 30 allows you to stay out for 30 times longer, or about 300 minutes. But that’s under lab conditions. In real life, you sweat, touch your face, swim, forget to reapply — and all of that reduces protection.

How Do Different SPF Numbers Actually Work?

SPF numbers do not increase protection proportionally. The difference between SPF 30 and 50 is much smaller than between 15 and 30. Here are approximate figures:

SPF 15 — blocks about 93% of UVB rays
SPF 30 — blocks about 97%
SPF 50 — blocks about 98%
SPF 100 — blocks up to 99%

See the pattern? Going from SPF 50 to 100 adds just 1% more protection. That doesn’t mean SPF 100 doesn’t work — but it doesn’t offer double the protection, as some might think.

Is High SPF Worth It?

Yes — but not for everyone and not always. SPF 50–100 may be helpful for:

People with very fair, sensitive, or problematic skin
After chemical peels, laser treatments, retinol, or acids
In tropical climates, mountains, or at the beach — anywhere with intense sun
Those who react to even small amounts of UVB exposure

But if you’re in the city, your skin doesn’t burn easily, and you apply SPF properly (enough product and reapply every 2 hours), then SPF 30 or 50 is completely sufficient.

Why Is More Not Always Better?

Feel on the skin. SPF 70+ formulas are often thicker, heavier, can leave a white cast, or clog pores.
False sense of security. People using SPF 100 often forget to reapply, thinking “It’s strong enough.” That’s a common mistake.
Cost and usage. Higher SPF usually means a higher price, but the added benefit is minimal.

How Much SPF to Use Daily?

For city life or office days — SPF 30 or 50
For active days outdoors, at the beach or in the mountains — SPF 50–100
If you’re using retinol, acids, or recovering from skin procedures — opt for SPF 50+

But most importantly: any SPF won’t work if you apply too little or don’t reapply throughout the day. Most people apply only ¼ of the recommended amount, which drastically lowers actual protection.

How to Apply SPF Correctly

Apply 15–20 minutes before sun exposure
Be generous — about ½ teaspoon for the face
Reapply every 2 hours, and after swimming, sweating, or towel-drying
Don’t forget ears, neck, around the eyes, and lips

Conclusion

The SPF number isn’t just marketing — but it’s also not an invincible shield. You don’t need the highest number possible, especially if it feels uncomfortable or doesn’t suit your skin. It’s better to choose SPF 30 or 50 that you’ll actually apply properly and reapply regularly. Even the strongest SPF 100 won’t help if it’s applied too thinly and only once a day.

So instead of thinking, “I need the highest SPF,” think:
“I’m going to use my SPF the right way.” — That’s real protection.