How Sunscreens Work II

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            There are two types of sunscreen chemicals available to us to help reduce this UV damage, and they are broadly categorized as: 

  • Organic sunscreens – these are made up of multiple carbon atoms bonded together, with long and complicated chemical names
  • Inorganic – also referred to as mineral sunscreens, and is the category that where Titanium Dioxide and Zinc Oxide full under

As mentioned in our previous post, organic sunscreens work by absorbing UV energy from sunlight, then converting it to less harmful forms of energy, like heat. How do they do this?

It helps to have a look at their chemical structures:

Their multiple hexagonal and pentagonal structures, along with their double and single bonds give these chemicals a special ability to allow electrons that it absorbs from the UV some space to “run” around and delocalize, which is the way by which it “tires out” the absorbed electrons.

Without getting too much into the nitty gritty, this method of delocalization is what allows UVA wavelengths to be absorbed by some chemicals, and UVB to be absorbed by others. Additionally, some newly developed chemical sunscreens have been found to be able to absorb in both UVA and UVB wavelengths quite efficiently, making them broad spectrum ingredients.

As for inorganic sunscreens, they largely in the same way: absorbing UV. They simply have an additional ability to scatter UV (about 5%). Given their inorganic nature, their UV absorbance capacity works a little differently than their organic counterparts.

Instead of starting out with an ingredient that stays at a stable or lower energy level until an outside force introduces something to excite it, what you have is tightly packed structure with a lot of electrons bunched together all interacting with each other, creating a lower energy band made up of a lot levels, and a higher energy band made up of a lot of levels as well.

This type of structure is allows what I would describe as a solid point at which it would absorb or scatter UV light, instead of a curve  that you would normally see with a inorganic sunscreen ingredient. Thus when you see the absorbance curve of Zinc Oxide and Titanium Dioxide, what you find is a drastic fall, simply because they stop absorbing at the shortest gap.

In addition to its ability to scatter light, inorganic sunscreen simply alters the direction that the UV is directed, in fact, it scatters UV towards your skin, where it hits another sunscreen particle and so on until it reduces the overall UV that gets on your skin.

Zinc Oxide absorbs both UVB and UVA, while Titanium Dioxide absorbs UVB and scatters UVA, and this is also dependent on the particle size used in a particular formula.

A common complaint with the use of these inorganic ingredients is the white cast it gives, and truthfully is the reason most people tend to steer away from using this option.

For those with skin sensitive skin, many may not have a choice with sunscreen options, the author would recommend trying nano-zinc oxide cream or lotion sunscreens as an alternative to purely organic sunscreen formulations. However, it would be best to avoid nanoparticle inorganic sunscreens in spray or powder form, in order to minimize risk of inhalation of these particles. 

As always, in order to get remotely close to the suggest protection level written on its label, one should ideally apply an even coat on bare skin 30 minutes before sun exposure, and to reapply every two hours, especially on areas where it could be wiped off, such as the back of your hands, ears, and neck.

If you liked this type of material, let us know in the comments below! Or if there are other topics you’d love to have discussed, send us a chat!

Credits to Michelle Wong, PhD, of Lab Muffin Beauty Science. Be sure to check her page out for more information on sunscreen.

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