UV light stability – why it is essential in sunscreen products
UV light stability basically means nothing more than ‘lightfast’ or ‘stable in UV light’.
In cosmetics, this term is mainly used in connection with sunscreens. A sunscreen must have high UV light stability, as products without sufficient stability break down very quickly under UV radiation and lose their protective effect. Studies have shown that the UVA protection provided by inferior sunscreen products can diminish significantly after only a short time. With increasing exposure, more and more UV radiation reaches the skin unhindered and can exert its harmful effects. Good UV light stability is therefore absolutely essential for every formulation in the sun protection sector.
Find out which substances ensure UV light stability here.
The UV light stability of sunscreen products is achieved by special UV filters. There are basically two types: mineral and chemical filters.
Mineral filters such as titanium dioxide and zinc oxide are considered particularly effective because they ensure excellent UV light stability and do not usually cause allergic reactions. Tiny nanoparticles of these substances are used in sunscreens so that the texture is easy to apply and does not leave an unpleasant film on the skin.
However, we have not used titanium dioxide for years, as this raw material is increasingly controversial for safety reasons. Titanium dioxide is now banned as a food additive – and since lip care products are considered food, we see a significant risk here. That is why we focus exclusively on zinc oxide as a non-nano UV filter.
Zinc oxide ensures reliable UV light stability, is significantly safer for health and, at the same time, enables modern, user-friendly formulations. Chemical filters such as methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT) or bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT) also offer excellent UV light stability.
They protect against both UVA and UVB rays and are difficult or impossible to penetrate the skin. However, there are differences here: while some mineral nanoparticles can partially overcome the skin barrier – possible long-term effects have not yet been conclusively researched – some chemical filters are suspected of having hormonal effects or promoting the formation of free radicals.
Important to know: Not all filters are recommended without reservation. In tests, substances such as 4-methylbenzylidene camphor (MBC), homosalate, octocrylene (OC), 3-benzylidene camphor and octyl methoxycinnamate (EHMC) were found to neither guarantee sufficient UV light stability nor have a satisfactory safety profile.
The search for new filters with UV stability
Although the number of approved filters with UV light stability appears sufficient at first glance, research into innovative alternatives is ongoing. Certain substances such as riboflavin, dihydroergotamine and chlorpromazine are naturally photo-unstable and lose their effectiveness under UV radiation. Reliable UV light stability can therefore only be achieved through the targeted use of special filters. International standards such as the ‘Guideline ICH Q1B’ serve to systematically test and document UV light stability.
Overview of the currently safest UV filters and their physical and chemical properties
- Zinc oxide (ZnO, non-nano)
- Type: Mineral UV filter
- UV range: Broad spectrum (UVA + UVB)
- Molecular weight: 81.38 g/mol
- Solubility: Insoluble in water, soluble in strong acids/bases
- Properties: White, crystalline powder, amphoteric behaviour
- Special features: Non-nano form is considered safe, hardly penetrates the skin, very high UV light stability
- Bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT)
- Type: Chemical broad-spectrum filter
- UV range: UVA-II + UVB
- Molecular weight: 823.04 g/mol
- Solubility: Oil-soluble
- Properties: Very photostable, highly effective even in low doses
- Special features: Considered one of the safest synthetic filters
- Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB)
- Type: Chemical UVA filter
- UV range: UVA-I (320–400 nm)
- Molecular weight: 563.73 g/mol
- Solubility: Oil-soluble
- Properties: Photostable, stabilises other filters in combination
- Special features: Excellent skin compatibility, complements UVB filters
- Ethylhexyl Triazone (EHT)
- Type: Chemical UVB filter
- UV range: Strong UVB protection (280–320 nm)
- Molecular weight: 823.04 g/mol
- Solubility: Oil-soluble
- Properties: Highest absorption capacity of all UVB filters, photostable
- Special features: Very efficient in low concentrations
- Disodium phenyl dibenzimidazole tetrasulfonate (AP)
- Type: Chemical UVA filter
- UV range: Mainly UVA-II (320–340 nm)
- Molecular weight: 608.41 g/mol
- Solubility: Water-soluble
- Properties: Crystalline powder, very photostable, ideal in aqueous formulations
- Special features: Provides reliable UVA protection, often combined with EHT, BEMT or DHHB to achieve full-spectrum protection
- Diethylhexyl Butamido Triazone (DHBT)
- Type: Chemical UVB filter
- UV range: UVB (280–320 nm)
- Molecular weight: 563.71 g/mol
- Solubility: Oil-soluble
- Properties: Very photostable, high molar extinction coefficient
- Special features: One of the most efficient UVB filters, very good skin compatibility
- Terephthalylidene Dicamphor Sulfonic Acid (TDSA)
- Type: Chemical UVA filter
- UV range: UVA-II (320–360 nm)
- Molecular weight: 562.7 g/mol
- Solubility: Water-soluble (unique among UV filters)
- Properties: High photostability, compatible with other filters
- Special features: Provides strong UVA protection, frequently used in premium sunscreens
- Phenylbenzimidazole Sulfonic Acid
- Type: Chemical UVB filter
- UV range: UVB (280–320 nm)
- Molecular weight: 315.31 g/mol
- Solubility: Water-soluble
- Properties: Photostable, good combination with oil-soluble filters
- Special features: Good skin compatibility, water-soluble component for light formulations
Conclusion: UV light stability determines effectiveness.
When purchasing sunscreen products, consumers should always look for very good UV light stability. Mineral filters are currently considered particularly promising as they offer a high level of protection and are comparatively safe. With chemical filters, on the other hand, it is advisable to check the ingredients carefully, as not all of them are classified as harmless.
Please feel free to contact us.
Our partner, Tojo Cosmetics GmbH, has already developed numerous innovative and UV-light-stable sunscreen products that combine maximum effectiveness with modern formulations.