We’ve already gone through basics about UV rays, protection against UV rays and everyday use of sunscreen. Now it’s time to take a look in the world of compounds that protect us from UV rays – UV filters.
There are two types of UV filters
Organic or chemical and inorganic or physical UV filters. Physical filters scatter and reflect UV rays, while chemical filters absorb them. Physical filters leave a white residue (unless they are nano size), while chemical filters spread quite smoothly.
Sunscreens are usually a mixture of different chemical and physical filters, because with combining them we achieve a broad spectrum protection.
There are even more UV filters then we mentioned in a previous post, so we asked members of a Slovenian Facebook group Ljubim kozmetike to mark the most common filters in their sunscreens. We are going to describe 4 most common ones.
Organic UV filters
Data from studies shows, that organic filters are present in most sunscreens on the market. The most common organic filter is Ethylhexyl methoxycinnamate, since it is present in 80% of all sunscreens. Chemical filters easily absorb in the skin and reach blood circulation. Consequently they can load in different tissues, liver and brain.
Oktyl metoxycinnamate (OMC) is a UVB filter known as 2-ethylhexyl-4-metoxycinnamate. As a compound it is allowed for usage in cosmetic products in United States and Europe in concentrations between 7.5-10%. Lots of studies suggest that OMC in an endocrine disruptor, because it can affect excretion of hormones.
After applying of cream with 10% concentration of OMC on the whole body (40g), the filter was absorbed in the skin and was later found in urine and blood. But if we take the highest measured concentration, the complete concentration in 4.7L of blood was only 0.002%.
The positive side of this filter is that it does not irritate the skin and does not cause sensibilisation.
Ethylhexyl salicylate or oktyl salicylate
It’s a organic UVB filter, that absorbs the UV rays. It is allowed for usage in cosmetic products in concentrations up to 5%. This is a filter with relatively good safety profile. Ethylhexyl salicylate possesses an ability to stabilize other photolabile (sensitive to light) UV filters and make them longer lasting. Quite a guy, ha?
This filter has a really low toxic profile. It does not cause irritation or sensibilization, it is not phototoxic and does not cause foto-allergies.
Inorganic UV filters
Inorganic filters used in sunscreens usually contain metal oxide particles, for example titanium dioxide and zinc oxide. These two can be used in concentrations up do 25%, but are usually contained in lower concentration – between 5-10%.
Chemical filters are still dominant in sun-protection products, but the number of products containing only physical filters is rising. One of the reasons why is the fact that they offer a broad spectrum protection – TiO₂ is more successful protection from UVB range, while ZnO is more successful at protection from UVA and UVB1 rays (the protection for UVB range is lower). Using these both filters together provides a broad spectrum protection. Another positive side of using physical filters is absence of irritation and limited skin penetration.
Dermal absorption is the main route of entrance for ZnO nanoparticles in our system. Most studies showed that ZnO particles don’t penetrate in deeper layers of the skin. Penetration is significantly higher when the skin barrier is damaged.
Titanium dioxide is commonly used as a white pigment in colors, plastic and paper and as an additive in food. Nanoparticles of TiO₂ are used because of the capability to absorb the UV light in sunscreen products. TiO₂ particles have very low toxicity.
Nanoparticles of TiO₂ can be used in sunscreen products in concentrations up to 25%. Studies show that particles of this filter don’t penetrate healthy or damaged skin. In human keratinocytes it exhibited almost no cytotoxicity, which suggest a very small toxic potential on the skin level.
Exposure to UV filters
We are most exposed to UV filters in a dermal way. Suggested application of sunscreen is 2mg/cm² skin, so that we would reach the protection factor listed on the product. This means we would have to use the whole 40g cream to protect the whole body. At this amount of product, the maximum penetration would be 5% for some organic UV filters. Studies show that amount of product applied is much lower than suggested (less than half). So if we apply a product with SPF 50, the real protection will be probably 25 or less.
UV filters offer a protection from erythema, actinic keratosis and carcinoma. There is also data that sunscreens block normal synthesis of vitamin D and that they act as endocrine disruptors. But in normal usage this is not the case.
What can we conclude?
Usage of UV filters is questionable from aspect of safety. More and more studies show the link between bigger usage of sunscreen products and phenomenon of hormonal and growth disorders. At this point you need to realize that in studies they work with much higher concentrations than allowed. With cosmetic products it is impossible to come in touch with such high concentrations. But we can’t just ignore what the studies say, because side effects can occur within sensitive population. Effects of being exposed to low doses of UV filters for a long period of time are pretty much unknown. Scientists should investigate further and try to find safer compounds to protect us from UV rays.