Creative Touch Permanent Makeup and Aesthetics

Sunscreen active ingredients divide into two regulatory and mechanistic categories: mineral filters (zinc oxide and titanium dioxide), which form a physical layer at the stratum corneum surface and are not systemically absorbed, and chemical (organic) filters, which are molecularly active UV absorbers that penetrate the stratum corneum and have been detected in plasma at varying concentrations. Both categories work primarily through UV absorption rather than reflection – the real clinical distinction is systemic bioavailability, not UV protection mechanism. The UK operates under the EU Cosmetics Regulation framework, which has approved a broader range of UV filters than the US FDA, including several next-generation broad-spectrum filters that offer superior photostability to many legacy chemical options. Ingredient selection in sunscreen formulation involves balancing UV coverage breadth, photostability, absorption profile, and tolerability – no single filter addresses all four optimally.

Sunscreen active ingredients are compounds included in topical formulations specifically to attenuate the UV radiation reaching viable skin tissue. The two broad categories – mineral (inorganic) and chemical (organic) filters – are distinguished by their chemistry, their regulatory status, their absorption behaviour at the skin surface, and to some extent the UV wavelengths they cover most effectively. Understanding the differences between them requires precision: the most widely repeated distinction in consumer skincare content – that mineral sunscreens work by reflecting UV whilst chemical sunscreens absorb it – is a significant oversimplification that obscures what the actual differences are and why they matter clinically.

The Mineral / Chemical Distinction

The terms “mineral” and “chemical” have become the standard consumer shorthand for two categories of UV filter, but neither term is entirely accurate. Mineral filters (zinc oxide and titanium dioxide) are inorganic compounds – they contain no carbon – whilst chemical filters are organic molecules, meaning they are carbon-based. “Physical” vs “chemical” is another common framing, implying that mineral filters work through physical blocking whilst chemical filters work through chemical absorption. This framing is also incorrect in the context of modern sunscreen formulations.

At the particle sizes used in contemporary mineral sunscreen products – typically micronised or nano-scale – zinc oxide and titanium dioxide primarily protect the skin through UV absorption and subsequent dissipation as heat, not through scattering or reflection. A 2016 study measuring reflectance and transmission of ZnO and TiO₂ using an optical integrating sphere found that reflection across the UV range averaged only 4–5%, with the remainder of protection provided by semiconductor band-gap UV absorption – concluding that mineral filters protect skin by absorption, not by reflection or scattering. ^[1]

The distinction that does matter clinically is systemic bioavailability: whether the active filter molecule penetrates the stratum corneum and enters systemic circulation. Mineral filter particles, regardless of size, do not penetrate beyond the outermost layers of the stratum corneum into viable skin tissue – they remain at the surface for the duration of wear. In-vivo nuclear microscopy studies on human skin biopsies found no TiO₂ or ZnO nanoparticles detectable in viable epidermal layers after up to 48 hours of occlusive exposure, a finding consistent across multiple studies reviewed by the TGA. ^{[2] [10]}

UV Coverage: UVA, UVB, and Broad-Spectrum

The solar UV spectrum reaching the skin surface divides into two clinically relevant bands:

UVB (290–320 nm) causes the acute effects most associated with sun damage – erythema, sunburn, and direct DNA pyrimidine dimer formation in keratinocytes. SPF ratings measure exclusively UVB protection. UVB is also responsible for vitamin D synthesis in the epidermis.

UVA (320–400 nm) penetrates more deeply into the dermis, driving photoageing through reactive oxygen species generation, collagen cross-linking and degradation, and indirect DNA damage. UVA is further subdivided into UVA2 (320–340 nm, the higher-energy portion with some overlap with UVB in its direct DNA damage mechanism) and UVA1 (340–400 nm, the longer-wavelength, deeper-penetrating portion responsible for the majority of photoageing effects). Standard SPF testing does not measure UVA protection; PA+++ ratings and the EU critical wavelength standard (≥370 nm) are the relevant measures for UVA coverage adequacy.

No single UV filter covers the entire UV spectrum comprehensively. Effective broad-spectrum protection almost always requires a combination of filters whose coverage profiles complement each other – which is why examining individual filter wavelength profiles matters when interpreting formulation ingredient lists. Zinc oxide is the closest to a complete single-filter option; avobenzone provides UVA1 coverage that most other chemical filters lack; titanium dioxide provides excellent UVB and UVA2 coverage but poor UVA1 coverage. Formulations combining these address the spectrum in a way no single ingredient can.

Systemic Absorption: What the Evidence Shows

Concerns about chemical sunscreen absorption gained significant clinical weight in 2019 and 2020 when two FDA-sponsored maximal use trials published in JAMA measured plasma concentrations of four common chemical filters – oxybenzone, avobenzone, octocrylene, and ecamsule – following application at the maximum real-world use conditions (full-body, four times daily for four days). All four filters were detected in plasma at concentrations above 0.5 ng/mL – the FDA threshold above which additional toxicological data is required before a GRASE (generally recognised as safe and effective) determination can be made. ^[4]

The critical calibration is that detection in plasma is not the same as evidence of harm. The FDA’s 0.5 ng/mL threshold is a data-gathering trigger, not a safety limit – it means “we need more data,” not “this is dangerous.” The oxybenzone endocrine disruption concern, for example, derives predominantly from in vitro studies and animal models using concentrations substantially higher than those measured in human plasma at real-world sunscreen use levels; a 2023 ToxCast comparison study found that oxybenzone’s in vitro endocrine activity was substantially weaker than some environmental chemicals already considered low-risk. ^[6] A 2025 systematic review of oxybenzone’s oestrogenic and androgenic activity confirmed that whilst in vitro activity is detectable, the evidence for clinically meaningful endocrine disruption at human exposure levels remains insufficient to establish causal harm. ^[7]

The honest position is that the absorption evidence warrants continued investigation and reasonable consumer choice to avoid specific filters – particularly in populations with higher sensitivity such as pregnant women, children, and those with hormonal conditions – without warranting the conclusion that chemical sunscreens are categorically unsafe. Avoiding UV exposure entirely carries a well-evidenced harm profile that no chemical sunscreen concern has currently matched.

Ingredient Reference

Mineral Filters

Zinc Oxide

Zinc oxide (ZnO) is an inorganic mineral filter and the most comprehensively broad-spectrum single UV filter available in consumer sunscreen formulations. Its UV absorption profile spans both UVB (290–320 nm) and the full UVA range including UVA1 (340–400 nm) – the longer-wavelength portion of UVA that drives the deeper photoageing effects that titanium dioxide and most chemical filters fail to adequately address. This makes zinc oxide the closest available approximation to a complete single-filter solution, and the primary mineral filter of choice when formulation simplicity is a priority. ^[8]

Particle size and the white cast problem. Traditional zinc oxide formulations used larger particles that scattered visible light, producing the characteristic white cast that limited cosmetic acceptability. Modern formulations use micronised or nano-scale zinc oxide (particle diameter typically 20–100 nm) that reduces visible-light scattering significantly, improving cosmetic elegance whilst retaining UV absorption efficacy. The nanoparticle question – whether smaller particles penetrate viable skin – has been examined in multiple studies. A 2016 review of topical nano zinc oxide skin penetration found that whilst nanoparticles may reach the deeper layers of the stratum corneum, penetration into the viable epidermis and dermis was not demonstrated in intact skin under normal use conditions. ^[3] A 2019 review supporting the safe use of zinc oxide nanoparticle sunscreens concluded that the weight of evidence supports their safety in topical application. ^[5]

Tolerability and clinical suitability. Zinc oxide is consistently among the best-tolerated UV filters, with anti-inflammatory properties that make it suitable for sensitised, post-procedure, and reactive skin. It does not require photostabilising co-ingredients in the way that avobenzone does, and carries no systemic absorption concern. These properties make it the default mineral filter recommendation for clients with reactive or compromised barrier skin, and the preferred post-treatment SPF filter in aesthetics contexts where chemical filter penetration of a disrupted barrier is a consideration.

Titanium Dioxide

Titanium dioxide (TiO₂) is an inorganic mineral filter with strong UVB and UVA2 absorption but limited coverage of UVA1 (wavelengths above approximately 360–380 nm). This spectral gap is titanium dioxide’s defining clinical limitation: used alone, it provides excellent protection against sunburn and the acute DNA damage of shorter-wavelength UV, but inadequate protection against the longer-wavelength UVA1 radiation primarily responsible for photoageing. It is rarely formulated as the sole UV filter in products making broad-spectrum claims for this reason. ^[8]

Complementarity with zinc oxide. The most common and mechanistically rational pairing in mineral sunscreen formulations is TiO₂ + ZnO – titanium dioxide providing strong UVB and UVA2 coverage that zinc oxide complements rather than duplicates, whilst zinc oxide extends coverage into UVA1 where titanium dioxide is weakest. This combination achieves genuinely broad-spectrum protection with two photostable ingredients and no systemic absorption concern from either component. Many well-formulated mineral sunscreens use this pairing at concentrations that allow each filter to operate near its optimal density without requiring either to compensate for the other’s spectral gap.

Photostability. Titanium dioxide is inherently photostable – it does not degrade on UV exposure in the way avobenzone does – and is frequently included in hybrid (mineral + chemical) formulations partly because its photostability extends the functional lifetime of less stable co-ingredients. It shares with zinc oxide the characteristic of remaining at the stratum corneum surface without systemic penetration.

Chemical Filters: Established Concerns

Oxybenzone

Oxybenzone (benzophenone-3, BP-3) is an organic UV filter covering UVB and short-to-mid UVA (280–350 nm). It is one of the most widely used chemical filters in legacy sunscreen formulations globally, and simultaneously the chemical filter with the most extensive safety concern literature. Its inclusion in both of the FDA maximal use trials confirmed plasma detection at concentrations exceeding 0.5 ng/mL – oxybenzone reached higher plasma concentrations than any of the other three filters tested, remaining detectable for up to three weeks after application ceased. ^[4]

The endocrine disruption concern centres on oxybenzone’s weak oestrogenic and androgenic activity observed in in vitro studies. As discussed in the systemic absorption section, the extrapolation from in vitro activity to clinically meaningful human endocrine disruption at real-world exposure concentrations has not been established by the current human evidence. The 2025 PMC systematic review concluded that oxybenzone demonstrates in vitro hormonal activity but that human epidemiological evidence for adverse endocrine effects at typical sunscreen use levels remains insufficient to support a definitive harmful classification. ^[7] The FDA classifies oxybenzone as requiring further data before a GRASE determination can be made – a position that reflects regulatory prudence under uncertainty rather than a finding of demonstrated harm.

For clients with hormonal sensitivities, during pregnancy, or in paediatric use, avoidance of oxybenzone in favour of mineral alternatives is a reasonable precautionary choice supported by the regulatory signal. For the general adult population, the risk calibration remains genuinely uncertain. Oxybenzone is also a documented contact allergen – photosensitivity reactions and contact allergic cheilitis from oxybenzone in lip products are recorded in the literature.

Octinoxate

Octinoxate (ethylhexyl methoxycinnamate, OMC) is one of the most widely used UVB filters in the world, providing effective coverage in the UVB range (280–320 nm) with high UV absorptivity. It has no meaningful UVA coverage, making it a UVB-only filter requiring combination with a UVA-active ingredient for any broad-spectrum claim. ^[9]

Octinoxate has been detected in plasma in the FDA maximal use trials at concentrations exceeding the 0.5 ng/mL threshold, and shares with oxybenzone some in vitro oestrogenic activity, though its hormonal activity signal in the literature is generally considered weaker. It is not GRASE-designated by the FDA. The EU Cosmetics Regulation permits octinoxate at up to 7.5% in cosmetic products. Octinoxate is also banned from sunscreen products in several coral reef protection jurisdictions (Hawaii, Palau, Aruba) due to evidence of coral bleaching toxicity at environmental concentrations. Whilst this does not directly affect UK consumer use decisions, it forms part of the reason some brands have moved away from octinoxate in reformulations.

Avobenzone

Avobenzone (butyl methoxydibenzoylmethane, BMBM) is the primary long-wavelength UVA filter available in most markets, with peak absorption at approximately 360 nm and meaningful coverage extending into UVA1 (up to ~400 nm). It fills the spectral gap that most other chemical filters – and titanium dioxide – leave at the longer UVA wavelengths responsible for photoageing. In this sense it is functionally important: without avobenzone or a next-generation broad-spectrum filter, many chemical-only sunscreen formulations are substantially under-protected in the UVA1 range regardless of their SPF rating.

Avobenzone’s critical limitation is photostability: it degrades significantly on UV exposure, losing a substantial proportion of its UV absorption capacity within an hour of sunlight exposure in its unprotected form. This photodegradation is not inert – degradation products are themselves potentially irritating and may include sensitising compounds. Formulation solutions to this problem have driven significant UV filter development: octocrylene is commonly used as an avobenzone photostabiliser, as are Tinosorb S (bemotrizinol) and specific polymeric photostabilisers. Formulations relying on avobenzone without a documented photostabiliser should be treated with scepticism regarding the durability of their UVA1 protection over a wear period.

Avobenzone reached plasma concentrations above the FDA 0.5 ng/mL threshold in the 2020 JAMA study. Its safety concern profile is considered lower than oxybenzone’s in the endocrine disruption literature, though the absorption data means it remains in the FDA non-GRASE category pending further data.

Octocrylene

Octocrylene is a UVB and short-UVA filter most frequently encountered in formulations not as a primary SPF contributor but as a photostabiliser for avobenzone. Its UV absorption profile partially overlaps with avobenzone’s excitation wavelengths in a way that interrupts avobenzone’s photodegradation pathway, making the combination of avobenzone + octocrylene substantially more photostable than avobenzone alone. Many mid-market chemical sunscreens rely on this pairing – avobenzone for UVA1 coverage, octocrylene to keep it functional. ^[9]

Octocrylene was included in the 2020 FDA maximal use trial and was detected in plasma above the 0.5 ng/mL threshold, though at lower concentrations than oxybenzone or avobenzone. A secondary concern with octocrylene is its hydrolysis behaviour: over time, particularly in products that have been stored or opened for extended periods, octocrylene can hydrolyse to benzophenone – a compound with its own endocrine activity signal and one that is not typically listed on the product label since it is a degradation product rather than an added ingredient. This is a formulation stability concern rather than an acute safety issue, but it is worth noting for clients using older products or those with high chemical sensitivity.

Next-Generation EU Filters

Tinosorb S and Tinosorb M

Tinosorb S (bemotrizinol, BEMT) and Tinosorb M (bisoctrizole, MBBT) are next-generation broad-spectrum UV filters approved under the EU Cosmetics Regulation but not currently approved by the US FDA – a regulatory gap that explains why European sunscreen formulations are frequently considered technically superior by informed consumers, and why “European sunscreens” have developed a strong following among skincare enthusiasts in the US who import them.

Tinosorb S is an organic broad-spectrum filter covering both UVB and the full UVA range with high molar extinction and strong photostability. Its key formulation role, beyond its own broad-spectrum coverage, is as an avobenzone photostabiliser – Tinosorb S accepts energy from excited avobenzone molecules before they can degrade, protecting avobenzone’s UVA1 coverage more effectively than octocrylene over extended wear. Formulations using Tinosorb S + avobenzone represent a significant improvement in UVA1 protection durability over avobenzone + octocrylene combinations. skintherapyletter.com

Tinosorb M is an organic-inorganic hybrid particle filter – its particles are large enough to remain primarily on the skin surface rather than penetrating, giving it an absorption profile more analogous to a mineral filter in terms of systemic bioavailability, whilst its organic chemistry provides the broad-spectrum absorption of a chemical filter. The combination of minimal penetration and broad-spectrum coverage makes Tinosorb M particularly relevant for clients seeking chemical-filter-level cosmetic elegance with reduced systemic absorption concerns. Neither Tinosorb S nor Tinosorb M has the systemic absorption profile of the legacy chemical filters – both are considered low-penetration relative to the oxybenzone/avobenzone/octinoxate group.

Mexoryl SX and Mexoryl XL

Mexoryl SX (ecamsule) and Mexoryl XL (drometrizole trisiloxane) are patented UV filters developed by L’Oréal, most commonly encountered in La Roche-Posay Anthelios formulations – products that a significant proportion of aesthetics clients and practitioners use as their reference-standard SPF. Mexoryl SX covers UVA2 (320–340 nm) with high photostability; Mexoryl XL covers a broader UVA range including some UVA1 and has a silicone backbone that contributes water resistance. Neither is approved by the FDA, though Mexoryl SX received limited FDA approval for one specific concentration in one product formulation.

The Mexoryl filters are relevant to this entity primarily because their photostability differentiates Anthelios formulations from the less stable avobenzone-primary alternatives. Mexoryl SX does not undergo the photodegradation that limits avobenzone’s functional UVA duration – a property that partly explains the consistent recommendation of Anthelios products by dermatologists seeking reliable UVA coverage in a photostable formulation. skintherapyletter.com Clients who use La Roche-Posay or similar EU-market SPF products are likely using one or both Mexoryl filters without being aware of it; understanding their role helps contextualise why formulation origin (EU vs US market) is a meaningful factor in SPF product selection.