SPF Explained: What Does SPF Number Mean

Nadia Podrabinek Nadia Podrabinek

Written by Nadia Podrabinek

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After writing several posts about beaches in Spain, I’ve decided to learn more about sunscreens and what SPF means. To my surprise, I knew very little about skin protection. So, I did some research and found a lot of helpful information, which I share with you now.

What is SPF?

SPF stands for Sun Protection Factor, used to label skin protection moistures. In other words, it is a UV (ultraviolet) radiation protection level. The higher the SPF value, the more effective the protection is. 

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As you might have learned from school, the primary source of ultraviolet rays on Earth is the Sun, exposing different types of radiation, including UV rays. 

Two of them negatively affect human skin: UVA and UVB rays.

1. UVA rays make up 95% of all ultraviolet radiation reaching the Earth’s surface and are the most dangerous for the skin. They initiate the process of destruction of collagen and elastin, damaging the dermis cells, eventually provoking malignant changes, and contributing to photoaging.

2. UVB rays make up only 5% of all ultraviolet reaching the Earth’s surface: most of them are being blocked by clouds and glass. UVB radiation penetrates the epidermis, due to which the skin not only tans but also gets a sunburn, which can provoke an allergic reaction or the development of cancer cells.

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The SPF number refers to how much of the incoming UV light will make it to your skin when you apply the cream properly (which is, according to wikipedia, 2 mg/cm2 ). So with SPF 15 you receive 1/15 of the UV, with SPF 30 you receive 1/30, etc. This means that the necessary exposure time to get a burn is increased by a factor of 15, 30, or whatever, assuming proper application, and that you don’t rub, wash, or sweat the cream away.


The SPF Sun Protection Factor, is a rating for protection as a multiplier of time.

If you skin takes 3,000 UV damage an hour at noon, SPF 100 means it should only gain 30 UV damage an hour at noon. Since most people aren’t vampires, SPF 30 is good for most situations.

It has nothing to do with how often to reapply, the sunscreen will wear off after a certain amount of time, usually two hours. When kayaking, I reapply when I can feel the ‘warmth’ of the sun again, which is a simple enough system. That’s also a good judge for if the SPF is high enough, the difference should be felt after applying it in sunlight.


Something I learned is: Spf 30 blocks like 90% of harmful rays. So spending a ton of money on higher spf isnt really worth it.

If you sweat, dry off and reapply. If you go swimming, dey off and reapply every 30-60 minutes depending on whiteness of skin. Normal activity without getting wet, id say reapply about evert 60-90 minutes.

Finally, sunscreen lotion is drastically better, but if you hate using it, getting the spray is better than nothing. But the spray coats thinner, is easier to wash off, lasts less time, and is usually more spotty.


It was originally meant to be a measurement of time.

i.e. If you take 10 minutes to burn without sunscreen then proper application of spf 30 sunscreen should make you burn at 300 minutes.

It’s a system that is obviously flawed by the fact that there are so many variables in conditions that make calculating a ratio like that impossible.


Which type of UV radiation is more dangerous?

Although only a small amount of UVB reaches our skin, this ultraviolet radiation is the most damaging to people, carrying a higher possibility of skin cancer.

What does the SPF number mean?

The SPF number on your sunscreen indicates the level of UVB radiation protection:

SPF numberAmount of UVB rays blockedTime to spend under the Sun safely
1090%50 minutes
1593%1 hour 15 minutes
3097%2 hours 30 minutes
50+98%4 hours
10099%5-6 hours

The numbers can be pretty complicated to remember, so you can use another simple formula. When using an SPF protection, multiply its number by 5 minutes to get the approximate time to stay under the sun (e.g., 10*5 = 50 minutes).

Keep in mind that real life is far more complex than any formula. The sunscreen must be applied in sufficient quantities, evenly distributed, and regularly reapplied (every 1 or 2 hours).

Explaining Mineral and Chemical Sunscreen Filters

Modern manufacturers include two types of UV filters in sunscreens: mineral and chemical.

Mineral sunscreen works like a mirror, reflecting the sun’s rays and keeping them away from the skin. Experts say it’s better to use mineral sunscreens if you have sensitive skin or if you are protecting a baby under six months. 

Unlike mineral ones, the chemical filters absorb sunlight radiation before UV rays damage the skin. Chemical filters are activated under the influence of ultraviolet radiation, destroying the energy of sunlight that is harmful to the skin. 

Lately, chemical formulas have been under pressure due to some investigations suggesting ingredients like oxybenzone being an eye irritant and skin allergen. FDA says it is safe to use chemical sunscreens.

Mineral filters

  • Reflect UVB and UVA rays,
  • Photostable, 
  • Act immediately after application,
  • Denser and thicker than chemical filter products,
  • Easy to wipe off with a hand or clothes as they lie on the skin surface,
  • Need to be reapplied periodically.

Modern mineral filters are increasingly used in the form of nanoparticles, do not whiten the skin, and provide better protection from the harmful effects of the sun.

Chemical filters

  • Transparent, do not leave a white cast,
  • Manage both UVA and UVB rays,
  • Take 15-20 minutes to start working.

Many people are afraid of chemical filters because of their “bad names” reputation. Chemical filters used to be not the safest, but the new generation has a larger molecular weight, penetrates the skin worse, and is safe for the skin and the body.

Why Spf Sunscreen Protection Is So Important?

Sunscreen helps us in several ways:

  • protects the skin from UVA and UVB rays,
  • prevents freckles and pigmentation,
  • reduces the likelihood of wrinkles,
  • protects skin collagen fibers from destruction, thereby maintaining skin elasticity,
  • most importantly, it prevents skin cancer.

Remember that the protection of sunscreens is not sufficient.

As a general rule of thumb, keep away from being directly exposed to the sunlight from 11 to 15, choose light cotton clothing with sleeves, wear hats, and protect your eyes with sunglasses.

Remember that the SPF protection of sunscreens is only an addition. As a general rule of thumb, keep away from being directly exposed to the sunlight from 11 to 15, choose light cotton clothing with sleeves, wear hats, and protect your eyes with sunglasses.

How to choose the right sunscreen?

First of all, you need to determine your skin phototype, then what auxiliary functions sunscreen should have: moisturizing, nourishing, matting the skin, etc.

The skin phototype

Skin phototype determines the degree of reaction of the skin to the effects of UV radiation and directly depends on its natural ability to protect itself. Any skin under the sun produces melanin pigment, which affects skin color.

There are 6 phototypes:

  • Phototype 1 (Celtic, people with albinism) – very light skin (milky white, porcelain), high sensitivity to ultraviolet radiation: reacts to the sun with redness, rarely tans, often covered with freckles. With this phototype, use products with SPF 50+.
  • Phototype 2 (Nordic, Scandinavian, Aryan) – light skin of ivory color, often with freckles, usually burns in the sun, a light shade of tan rarely appears. With this phototype, use products with SPF 30-50.
  • Phototype 3 (European) – slightly dark skin, practically does not burn. The tan appears gradually and evenly. With this phototype, use products with SPF 20-30.
  • Phototype 4 (Mediterranean) – olive-colored skin without freckles burns minimally. The tan lies evenly. With this phototype, use products with SPF 15.
  • Phototype 5 (Indonesian) – dark brown skin, rarely burns, tan appears as a rich dark shade. With this phototype, use products with SPF 5-10.
  • Phototype 6 (African) – very dark chocolate-colored skin, low sensitivity to ultraviolet radiation: it never burns, and the tan is very dark. With this phototype, use products with SPF 5.

What Type of Sunscreen Is Best for My Skin?

To preserve the beauty of the skin, choose SPF protection based on the needs of your epidermis:

  • Oily skin: choose light texture products (fluid, milk, gel) with mattifying non-comedogenic formulas. 
  • Dry skin: choose non-greasy creams and oils with moisturizing and softening formulas.
  • Sensitive skin: choose light textures (milk, cream, gel) with hypoallergenic formulas and soothing effect. To protect the delicate area around the eyes and lips, also choose sunscreens for hypersensitive skin, for example.

Which SPF Level should I use?

Many scientists and dermatologists say that you should use the SPF 30 or higher in most situations under the sun.

Which SPF number should I use if I have darker skin?

It is okay to use an SPF between 15-30 for this type of skin (pigmented skin). This skin is more protected due to higher amounts of melanin.

What does Broad-Spectrum Protection mean?

It means what it says, the protection from both UVA and UVB rays.

Can you tan while wearing sunscreen?

The answer is yes, you can. There are no sunscreens with 100% protection, and no SPF product can give you complete protection. 

Best Sunscreens in 2022

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Photo by Rafaella Mendes Diniz 

Best Sunscreens for Oily Skin

  • La Roche-Posay Anthelios. SPF 50+
  • Kiehl’s Ultra Light Daily UV Defense. Mineral Sunscreen. SPF 50
  • Paula’s Choice Extra Care Non-Greasy Sunscreen. SPF 50
  • EltaMD UV Clear Broad-Spectrum. SPF 46
  • Shiseido Clear Sunscreen STICK. SPF 50+
  • Supergoop Unseen Sunscreen. SPF 40
  • Cay Skin Universal Mineral Face Lotion. SPF 55
  • Bliss Block Star Invisible Daily Sunscreen. SPF 30
  • Shiseido Urban Environment Oil-Free Sunscreen Broad-Spectrum. SPF 42
  • SkinMedica Essential Defense Mineral Shield Broad-Spectrum. SPF 35
  • Juice Beauty Oil-Free Moisturizer. SPF 30

Best Sunscreens for dry skin

  • Neutrogena Ultra Sheer Sunscreen
  • Earth Rhythm Mineral Sunscreen 
  • Village 11 Factory Hydra Sun Fluid. SPF 50+
  • Bioderma Photoderm MAX Aquafluide. SPF 50
  • Eucerin Sun Crema Sensitive Protect. SPF 50+
  • Glowscreen Sunscreen Broad Spectrum. SPF 40
  • Shiseido ultimate sun protector lotion. SPF 50+
  • La Roche-Posay Anthelios Ultra-Light Invisible Fluid. SPF 30
  • CeraVe AM Facial Moisturizing Lotion. SPF 30
  • Aveeno Positively Radiant Daily Facial Moisturizer

Best Sunscreens sensitive skin

  • ISDIN Foto Ultra 100 Spot Prevent Fluid. SPF 50+
  • Biossance Squalane + Zinc Sheer Mineral Sunscreen. SPF 30
  • CeraVe Tinted Mineral Sunscreen. SPF 30
  • Avène Solaire UV Mineral Multi-Defense Sunscreen Fluid
  • Neutrogena Sensitive Skin Mineral Sunscreen Broad Spectrum. SPF 60
  • EltaMD UV Restore Broad-Spectrum. SPF 40
  • Shiseido Ultimate Sun Protection Lotion WetForce for Sensitive Skin and Children. SPF 50+
  • Shiseido Expert Sun Protector Lotion. SPF 30
  • Aveeno Mineral Sensitive Skin Sunscreen
  • Cocokind Daily SPF

Best Sunscreens for everyday use

  • Heliocare 360º Mineral Tolerance Fluid. SPF 50
  • Avène’s Solaire UV Mineral Multi-Defense Sunscreen. SPF 50+
  • La Roche Posay Toleriane Double Repair. SPF 30
  • Shiseido Expert Sun Protector Lotion. SPF 30

Best Sunscreens for body

  • Lotus Safe Sun UV Protect Body Lotion. SPF 25
  • Wow Skin Science Sunscreen Matte Finish. SPF 55
  • Himalaya Herbals Protective Sunscreen Lotion. SPF 15
  • Avene Very High Protection Spray. SPF 50
  • VLCC Water Resistant Sunscreen Gel Creme. SPF 60

Check sunscreens prices at Amazon.

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