Sunscreen Basics

Woman applying sunscreen by pool

What are the different types of sunscreens?

Chemical Sunscreens

Chemical sunscreens absorb UV rays and convert them into heat- preventing penetration into the deeper layers of the skin. Examples include avobenzone, octinoxate, and oxybenzone.

Physical Sunscreens

Physical sunscreens are made of micronized pieces or metal like zinc and titanium that form a layer on the skin’s surface to protect it from UV rays. These are also called mineral sunscreens. Physical sunscreens block both UVA and UVB rays. However, they do not protect the skin from all of the wavelengths of UVA and are therefore often combined with chemical sunscreens.

Mineral sunscreens are often white and not as spreadable as chemical sunscreens but are considered safer for the body and environment. Examples include zinc oxide and titanium dioxide.

Organic sunscreens

All organic and natural sunscreens are made from zinc oxide or titanium dioxide. They may have plant-derived antioxidants included in them as well. 

How is SPF calculated?


Before we continue, please note that the rules about SPF labeling are different in various countries and that the following information is based on the sunscreen labeling rules in the USA.

Chemical and physical sunscreen ingredients prevent redness caused by ultraviolet exposure. The SPF labeling process is strictly regulated by the FDA and in order to put an SPF number on a skincare product label studies must be done.

The sun protection factor (SPF) represents how much ultraviolet light B can be shone on the skin before redness occurs. 

SPF number is measured by placing 2mg / cmof sunscreen on human skin, usually the buttocks area (if it's a cream, the amount is about 0.4 ounces of the cream). The area is then exposed to a certain amount of UVB light and the amount of redness is measured in the sunscreen-covered area versus the other side of the buttocks that does not have any sunscreen applied (the control side). The difference between the dose of UVB required to cause redness on the sunscreen side versus the control side is the SPF. For example, an SPF 15 sunscreen means that it takes 15 times the amount of ultraviolet B to turn the skin red. The amount of UVB required to turn the skin red is called the MED (minimal erythema dose).

SPF does not measure UVA protection

There isn't a recognized or agreed-upon standard for measuring UVA-containing sunscreens in the US, so the SPF always applies to protection from UVB. This is because each large company has its own way of measuring UVA protection, and no one has been able to agree on which is best so the FDA has not set the measuring standards. It seems that they do not want to favor one company over another because the company that did not use the chosen standard would have to repeat all of their sunscreen tests. This is unfortunate for us because we do not know how well sunscreens protect us from UVA in the US. The only other options are to buy European sunscreens or to look for “Broad Spectrum Sunscreen” which protects from both UVA and UVB rays.

How much SPF should I use to get the SPF on the label?

Most people only use 25% of the necessary amount of SPF to meet the SPF on the label.  This means that an SPF of 15 is not really 15 because not enough was applied which is why you are told to use higher SPF levels.

You must use at least ¼ teaspoon of SPF for your face to achieve the SPF on the label and you should reapply after water immersion, excess sweating, and at least every hour.

UVA vs UVB Sunscreens

The United States has few sunscreen choices than other parts of the world.  Of US-approved sunscreens, only Avobenzone (Parsol) blocks the entire spectrum of UVA (310nm to 400nm).

Zinc oxide blocks both UVA and UVB rays, while titanium dioxide provides better UVB protection than zinc oxide.  This is why zinc oxide and titanium dioxide are often used together.[1] [2]

 This sunscreen ingredient table lists sunscreen ingredients and which wavelengths of UV they block.


What is the Best Sunscreen in the World?

The sunscreens that have the best broad-spectrum UVA and UVB protection are chemical sunscreens. However, these have other issues such as environmental safety, risk of allergy, and instability of sunscreen ingredients.

Sunscreens are often used together to boost protection. One example is Cell Ox Shield which contains the sunscreen ingredients: Avobenzone, Homosalate, Octisalate, Octocrylene, and Oxybenzone. Although Cell Ox Shield is found in Anthelios sunscreens, it is not the same as the Mexoryl SX, Mexoryl XL, and Tinsorb S-containing sunscreens called Antherios found in Europe and Canada.

Our Opinion On Sunscreen Filters

For daily use, choose a natural mineral sunscreen for the face containing these ingredients:

  1. Zinc oxide - One of the best sunscreen choices because it is natural/non-toxic to humans and the environment, and it also protects from UVA and UVB rays. It has a low risk for irritation. Micronized looks less white on the skin. 
  2. Titanium Dioxide - A natural mineral sunscreen that reflects UV radiation away from the skin that is also natural/non-toxic to humans and the environment. Best when combined with zinc oxide.
  3. Iron Oxide - A natural mineral that blocks blue light from phones and computer screens that is used to give a tint to sunscreens. This is why tinted sunscreens provide more sun and light protection than non-tinted sunscreens. 

Our favorite mineral-based physical non-comedogenic tinted sunscreens for the face are:

For prolonged outdoor sun exposure, you may choose a chemical sunscreen for the face to increase UVA and UVB protection. However, every chemical sunscreen has a downside:

  1. Avobenzone (Parsol) - has the best protection, but it stings. Rosacea skin types often get irritated by avobenzone. If you are going to be sweating a lot, it can run into your eyes and burn. Our advice is to either a. do not put this avobenzone-containing sunscreen on your forehead (wear a cap and choose a different sunscreen for the forehead) or b. do not use this when you expect to sweat a lot.
  2. Octinoxate - Octyl methoxycinnamate is a UVB absorbing ingredient that is added to boost UVB protection in chemical sunscreens. Although many studies have shown it is safe for humans and coral reefs, it is a controversial ingredient because some studies have suggested it is toxic to reefs and may have endocrine effects. Although the risk is small, we recommend not using Octyl methoxycinnamate-containing sunscreen in the ocean, on large areas of the body, or on children under the age of. Many people also have photoallergy to octinoxate. 
  3. Octisalate - Only has UVB protection, no UVA protection.

The Bottom Line

I have very allergic sensitive skin, so I can only use mineral sunscreens. But since my skin is dry, I also want a sunscreen that is hydrating and tinted to help even out my skin tone.  So, for my DSNW 4 Skin Type, the sunscreens I prefer are: 


Whichever SPF you choose, remember these important tips:

  1. Wear it every single day
  2. Apply at least 1/4 teaspoon of sunscreen to your face
  3. Reapply after getting wet or sweating
  4. Reapply every hour
  5. Don’t rely on powder SPFs or the sunscreen within your foundation
    1. You can use an SPF powder or SPF-containing foundation over top of your main sunscreen, but for optimal protection do not use it alone.


[1] Schneider, S. L., & Lim, H. W. (2019). A review of inorganic UV filters zinc oxide and titanium dioxide. Photodermatology, photoimmunology & photomedicine35(6), 442-446.

[2] Antoniou, C., Kosmadaki, M. G., Stratigos, A. J., & Katsambas, A. D. (2008). Sunscreens–what's important to know. Journal of the European academy of dermatology and venereology22(9), 1110-1119.


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