29/05/2013, by

Summer is nearly here: Time for sun lotions (and their chemistry!)

I love Spring: sun shines, birds sing, flowers blossom, everything is surrounded by colourful landscapes… and summer is round the corner (although it seems that corner is far away!).

Perfect timing for this post: The chemistry of sun lotions.

If you are getting ready to go to the beach, for a ride or a trek in the mountains, something that you must not forget is your sun lotion. Fortunately, people are becoming increasingly more aware of the use of sun creams, and hopefully this post will help.

Do you know what’s behind the tiny white layer of lotion on your skin? Continue reading this blog post and you’ll find out.

- Do we really need sun lotions?

Ooooh, yes (and I promise I have nothing to do with sunscreens companies).

Our skin has some pigments that protect us from sun radiation. However, those natural pigments do not protect us from some specific and damaging radiations produced by the sun: The ultra-violet radiation or UV-radiation. Therefore, we need some extra help to be protected against it.

UV radiation can be divided in two sub-types of radiation:

  • UV-B radiation (wavelength 280-315nm) that causes burning of the skin. It damages the upper layer of the skin, known as epidermis.
  • UV-A radiation (wavelength 315-400nm) that causes premature aging of the skin, as it damages the deeper layer of the skin, or dermis.

Both types of radiation have been linked to skin cancer.

UVA and UVB radiation

- So, how do sun creams work?

In recent times, we can have sun creams in a variety of formats: gel, lotion, sprays… and they all work on the same way.

All of them contain a range of UV filters that protect the skin from the UV radiation, both inorganic filters such as titanium dioxide (TiO2) and zinc oxide (ZnO)and organic filters, mostly aromatic molecules conjugated with carbonyl groups.

These filters reflect, scatter and absorb UV-radiation. So, when we apply the sun lotion on our skin, we are spreading a bunch of UV filters dispersed in an oily and watery cream that deviate or absorb the damaging radiation from our skin.

Zinc oxide (ZnO) is superior to titanium dioxide (TiO2) at wavelengths between 340 and 380 nm and it is better against UVA radiation protection.

Let’s look now at the organic filters, the conjugated organic molecules.

Example of a conjugated organic molecule

In conjugated organic molecules, the electrons are spread over the molecule, so the bonds within the molecule are weaker and, therefore, more easily broken. The energy provided by the sun UV rays is the right amount of energy to break these weak bonds in the organic molecules. When these bonds break, the molecules become very reactive and transform into other products.

So, the organic conjugated molecules of sunscreens absorb UV rays to be transformed into other products, preventing the ultraviolet rays from being absorbed by your skin.

Sun lotion protection against UV radiation

- What SPF should I look for?

The SPF (Sun Protection Factor), broadly speaking, indicates how long you can stay in the sun without burning. If normally, you can stay in the sun without burning for 10 minutes, with sun lotion on of SPF 15 you’ll be able to stay in the sun without burning 15 times longer, therefore 150 minutes. This is a rough approximation that assumes that the intensity of UV radiation of the sun is always the same, which is not true.
The solar radiation varies considerably with several factors:

  • The time of day: Sun rays are the strongest between 10 am and 4 pm.
  • The altitude and latitude: Sun rays are stronger at higher elevations and at latitudes near the equator.

The SPF only applies to UVB radiation, the one that causes burns – that is why they define it as ‘the time you can stay in the sun without burning’. Sun creams that also work against UVA radiation will have a ‘Broad Spectrum’ label (protection against both types of radiation UVB/UVA).


- So…

Summer is great and sunny days are amazing BUT we now know that the sun produces damaging radiation, UV radiation, and we do not have natural pigments that fully protect us (our skin) against it. Therefore, enjoy the sun and your summer holidays but do not forget your sun lotion. Pay attention to the SPF number and apply the lotion accordingly (better more often than less) because titanium dioxide, zinc oxide and organic molecules will protect your skin.

Chemistry is good.

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1 Comment

  1. #1 for Margot - 29 May 2013 - 12:14

    Great post and very interesting Lorena! This is what I tried to explain to my dutch brother but he didn’t listen to me and obviously he burnt his skin, especially feet skin which is really delicate (and most of the times people forget to use the cream there…). But, a good remedy, if you have it at home, is pure aloe vera gel extracted directly from the plant. Tested! ;-)

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