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Sun filters

Sun filters: physical and chemical

25 October 2022

Sunlight is composed of different radiation with different wavelengths. The most harmful to the skin is ultraviolet (UV) radiation. For this reason, it’s important to use products with sun filters.

UVA are the rays most present in sunlight, they account for about 95 per cent of UV radiation, have a high wavelength and also pass through cloudy skies. They make a minor contribution to tanning and the appearance of erythema and sunburn, however, as they penetrate into the deeper layers of the epidermis, they disrupt elastic and collagen fibres. This is why they are considered the main culprits of skin photo-ageing.

UVB rays, on the other hand, have a shorter wavelength than UVA and act mainly on the surface, at the level of the epidermis, stimulating the production of melanin. They promote a long-lasting tan but, being more powerful, can cause sunstroke, erythema and sunburn without adequate protection. Although UVB does not reach the dermis, the deepest layer of the skin, it also contributes to skin ageing.
This is why sun cosmetics must provide good protection from both UVA and UVB.

Sun filters are divided into two macro-categories:
  • Physical filters
  • Chemical filters

Physical filters consist of very fine inert particles that are able to reflect the sun’s rays. Consequently, physical filters create a physical barrier that can repel radiation without being modified. In this category of filters we find natural clays such as zinc oxide and titanium dioxide and synthetic molecules. Due to their mechanical action, they are able to protect the skin from both UVA and UVB radiation. The great disadvantage of this category of filters is precisely their inert nature, which means that they remain suspended in the formulation without dissolving in it; the presence of these suspended particles gives rise to the annoying white trail during product application.

Chemical filters, also called organic filters, are molecules of natural or synthetic origin that are placed on the skin and are able to absorb and break down the sun’s radiation, protecting the skin by a chemical and not physical mechanism; this difference with physical filters means that chemical filters act selectively on either UVA or UVB rays. This is why it is essential to study a filter composition that provides complete protection in order to safeguard the health of our skin. These substances, depending on their nature, dissolve in the aqueous or oily part of formulations, making them more comfortable and easier to spread than their counterparts with physical filters.

In light of this information, Gen-Hyal chose to formulate a sunscreen based on chemical/organic filters in order to create a product with a pleasant, fluid texture and complete coverage from UVB and UVA rays.

An important aspect for our safety in the sun is the photostability of sun filters to radiation.

Chemical filters absorb solar energy and then release it in the form of heat, possibly without being affected by the radiation itself. Filters that are not very photostable, once they have absorbed the radiation, are quickly damaged and no longer fulfil their function. If the sun filter degrades, it often produces free radicals and harmful substances, and if the sun filter is absorbed deep into our skin, these free radicals and harmful substances can damage proteins and DNA, accelerating the photo-ageing processes of the skin. In a high-quality formulation these damages can be prevented by the abundant presence of antioxidants (e.g. vitamin E) in the formula that block these free radicals before they cause damage.
Sun protection factor is a number that defines the skin’s ability to defend itself against solar radiation, particularly UVB radiation. This number is commonly referred to as SPF, which stands for Sun Protection Factor.
The meaning of this number is identified as an exposure dose (duration x radiant power x area) that is a multiple of the dose that produces erythema. That is, an SPF 50 should lead to sun erythema with an exposure dose 50 times higher than that expected in the absence of protection. By definition, the SPF uses a biological marker, the erythema. To a good approximation, in the first few minutes after application, the SPF can indicate the amount of radiation filtered out by the product. An SPF 50 would let through no more than 1/50th of the solar radiation or 2%, stopping 98% of it. An SPF 30 would let through no more than 1/30 (or 3.3%), stopping just under 97% of it.

But there is another aspect to consider: as the filter degrades, the sun protection factor of the product decreases. The effect of loss of SPF during sun exposure depends on the photostability of the sun filters: with very photostable filters the phenomenon is of negligible importance, but with poorly photostable filters, unfortunately very common in commercially available sunscreen products, the phenomenon can be very significant. Therefore, a high-quality formulation with photostable filters is the ideal choice for safe protection, but the advice that still applies is to repeat the application of the product several times during the day, especially in the case of children.

Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine, for example, is an extremely photostable filter that also stabilises the other filters in the formulation.
The filters contained in our Gen-Hyal Anti-Age UV SHIELD SPF 30+ formulation are:

  • Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB): this is a photostable filter that protects the skin from UVA rays.
  • Ethylhexyl Methoxycinnamate (EHMC): is a UVB filter that also helps solubilise other filters in the formulation to prevent re-crystallisation and consequently inadequate protection.
  • Ethylhexyl Triazone (EHT): a highly photostable UVB filter.
  • Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine (BEMT): broad spectrum organic filter that also stabilises the other filters in the formulation for long-lasting protection.

The synergy of these sun filters results in a complete formulation that offers long-lasting UVA and UVB protection in a product that is pleasant to use every day of the year, even in winter.

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