Yes. Contrary to Popular Belief, Today’s Micronized Zinc Oxide and Titanium Dioxide Sunscreens Primarily Absorb UV Radiation, Just like Their Chemical Sunscreen Cousins
The Essential Info
In the past, chemical sunscreens (avobenzone, homosalate, octinoxate, octisalate, octocrylene, oxybenzone) worked by absorbing the sun’s rays, while physical sunscreens (zinc oxide and titanium dioxide) commonly reflected and scattered the sun’s rays.
Today, with the advent of micronized physical sunscreens, both chemical and physical sunscreens now protect the skin from the sun mainly by absorbing UV light.
Excessive sun exposure can be damaging to the skin, which is why it is a good idea to wear sunscreen when spending long periods of time outside. This is particularly important if you are undergoing certain acne treatments, such as isotretinoin (Accutane®) and antibiotics, which can increase the skin’s sensitivity to the sun.
Chemical and Physical Sunscreen Active Ingredients
- Chemical sunscreen ingredients: So-called “chemical” sunscreen active ingredients include all sunscreen ingredients except for zinc oxide and titanium dioxide. The ones most commonly used in the United States are (in alphabetical order):
- Physical sunscreen ingredients: So-called “physical” sunscreen ingredients include only these two:
- Titanium dioxide
- Zinc oxide
Many people believe that chemical sunscreen ingredients protect the skin by absorbing UV light, whereas physical sunscreen ingredients do not absorb UV light but, instead, reflect and scatter it. This was true in the past, but is no longer the case. Let’s look at it in historical context so it makes more sense.
Chemical sunscreen ingredients: Historically, chemical sunscreens have always worked by absorbing UV light before it can reach the skin, and continue to work in this same way.
Physical sunscreen ingredients: Historically, manufacturers were only able to produce zinc oxide and titanium dioxide in large particle sizes that appeared opaque/white when applied on the skin. Because they had such large particle sizes, they were able to reflect and scatter UV light away from the skin, and also absorb some UV light. However, since the advent of smaller, micronized zinc oxide and titanium dioxide particles that allow the sunscreen to appear more-or-less transparent when applied on the skin, they now work primarily by absorbing UV light.
So, in today’s sunscreens, both chemical and physical sunscreen ingredients work primarily by absorbing UV light.
In the real world, the right mix of sunscreen ingredients of either type will protect you from the sun, but it is important to reapply sunscreen every two hours or so to maintain adequate UV protection for your skin. This is particularly vital with chemical sunscreen ingredients, which break down over time in the sun.
How chemical and physical sunscreen ingredients protect the skin from the sun
Even though both chemical and physical sunscreen ingredients protect the skin mainly by absorbing UV rays, there remain subtle differences in how they work. Let’s look at this more closely.
Whenever sunlight hits any substance, there are three possibilities for what can happen:
- The substance can absorb the light
- The substance can reflect the light
- The substance can scatter the light1
- Chemical sunscreen ingredients: When it comes to sunscreens, chemical sunscreen ingredients only absorb UV light.
- Physical sunscreen ingredients: On the other hand, today’s physical sunscreen ingredients primarily absorb UV light, but physical sunscreen ingredients also reflect and scatter some of the UV light.
Both chemical and physical sunscreens consist of chemicals
Actually, the terms “chemical” and “physical” are somewhat misleading, because both types of sunscreens consist of chemicals. In fact, every substance is made of chemicals, including water. However, the chemicals that chemical and physical sunscreens contain are different.
- Chemical sunscreen ingredients: So-called “chemical” sunscreen ingredients consist of organic chemicals, which means substances that contain carbon.
- Physical sunscreen ingredients: So-called “physical” sunscreen ingredients consist of inorganic chemicals–in other words, substances that do not contain carbon.
Thus, a more exact name for chemical sunscreen ingredients would be “organic” sunscreen ingredients, and a more exact name for physical sunscreen ingredients would be “inorganic” sunscreen ingredients.
This is an important difference, because organic and inorganic chemicals tend to behave in unique ways, and this also applies to sunscreen ingredients. In other words, although chemical and physical sunscreen ingredients both work primarily by absorbing UV light, they accomplish this in different ways.
- Chemical sunscreen ingredients:
- Chemical sunscreen ingredients are molecules that contain a special structure called a chromophore. This structure absorbs UV light.
- Some sunscreen ingredients contain a chromophore that only absorbs UVA light. Others contain a chromophore that only absorbs UVB light. For this reason, manufacturers often combine multiple chemical sunscreen ingredients to create a broad-spectrum sunscreen, which protects the skin from both UVA and UVB rays.
- Some chemical sunscreen ingredients are photostable, which means they continue to function well after long periods of exposure to UV light.
- Other chemical sunscreen ingredients are photounstable or photolabile, which means they break down after some time in the sun. Once these ingredients break down, they no longer protect the skin from UV light. This is the main reason why it is important to reapply sunscreen that contains chemical sunscreen ingredients every two hours or so.
- Physical sunscreen ingredients:
- Physical sunscreen ingredients are actually tiny crystals. These crystals absorb UV light.
- The size of the crystals determines how much light, if any, the physical sunscreen ingredients reflect and scatter. Small crystals mostly absorb UV light. Larger crystals, such as those used in physical sunscreens in the past, reflect and scatter more light.
- All physical sunscreen ingredients are photostable, which means that, unlike some chemical sunscreen ingredients, they do not break down after exposure to UV light
- Some physical sunscreen ingredients are photoreactive, which means they can react with chemicals in the air or with other ingredients in the sunscreen formulation to form harmful substances called free radicals. However, manufacturers today usually coat physical sunscreen crystals with non-reactive substances to prevent this.
How chemical sunscreen ingredients protect the skin from the sun: The full scoop
How physical sunscreens protect the skin from the sun: The full scoop
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