Summer is here! The sun is shining and it is hot! With the ever-increasing frequency of heatwaves that we’re experiencing it is no surprise that there has been a trend for the beauty industry to innovate toward multi-functional suncare products that double as skincare. Higher-end suncare formulations now routinely include active ingredients often found in skincare like vitamin C, niacinamide, hyaluronic acid and panthenol alongside UV filters. The implication of this is that there are more chemicals being applied to skin, more frequently, and specifically in conditions where skin is being exposed to direct sunlight.
As these formulations are becoming more sophisticated, it is increasingly important to demonstrate both a suncare product’s protective function and that the claims linked to its skincare properties are supported by strong data. That’s where XCellR8 can help. Our human-relevant, animal-free testing services support developers in ensuring increasingly complex formulations are mild and non-irritating to the skin and eyes, while also providing evidence for skincare-relevant claims such as antioxidant activity, maintenance of barrier integrity and collagen boosting.
However, with suncare, the technical requirements and function of the product also need assessing. Here are some points that should be considered when developing suncare products:
Active Ingredients in Sunlight
When active ingredients are incorporated into products designed for sun exposure, there’s an additional layer of exposure assessment to consider. The question isn’t just whether an ingredient is safe at rest, but whether it behaves differently when applied to skin that’s actively receiving UV radiation. A safety assessment should evaluate whether UV exposure could alter the bioavailability or stability of each active, and whether these breakdown products cause increased skin irritation or sensitisation. This risk is further amplified by usage instructions that direct wearers to apply the product multiple times throughout the day, including during periods of direct sun exposure.
Moreover, sunburn and other forms of skin microdamage, including that associated with sweat and dehydration in hot weather, may further increase this risk by compromising the skin barrier and increasing permeability. This can allow ingredients that would normally remain within the stratum corneum to penetrate into the viable epidermis and potentially enter systemic circulation.
Systemic Absorption: The Regulatory Picture
Recent research has proven that several organic UV filters, including oxybenzone, octinoxate, octisalate, homosalate, avobenzone and octocrylene, readily penetrate the skin and are detected in bloodstream, urine and breast milk after repeated application. In a 2020 FDA study, absorption levels of avobenzone and other filters exceeded the agency’s proposed safety threshold. Octisalate has been detected in urine at concentrations 10 times above the FDA’s established cutoff for systemic exposure following a single full-body application.
Some of these filters have potential endocrine-disrupting effects. Octinoxate was identified by the European Commission in 2024 as endocrine-active, though the Commission concluded it remains safe at current regulatory limits (up to 10%). Homosalate and other filters are undergoing ongoing evaluation by regulatory agencies for long-term safety at typical usage levels.
These few examples demonstrate the need for expanded regulatory scrutiny of what happens when chemical actives accumulate in the body from repeated daily application.
Exposure and Chemical Load
The marketing around suncare often emphasises reapplication is required four to six times daily and more so if enjoying common summer activities, such as swimming. Each application presents a reset of the chemical load on the skin and the body’s detoxifying systems. When one product contains multiple UV filters plus additional actives (e.g. brighteners, hydrators, antioxidants), and when consumers are layering multiple suncare products simultaneously, such as applying existing skincare and makeup containing SPF, then cumulative exposure calculations become complex and difficult to model in conventional safety assessments.
There’s no established framework for evaluating how the body’s cytochrome P450 system handles repeated doses of complex cosmetic formulations. The science of exposure assessment has historically focused on single ingredients at single timepoints, not the repeated multi-product scenarios that are now standard marketing practice.
Interactions Between Products
The potential for unintended synergistic interactions between ingredients across multiple products is a related concern. When a consumer applies a vitamin C serum, then a niacinamide sunscreen, then a hydrating powder with mineral filters and additional actives, there’s limited data on how those combinations behave systemically.
What This Means for Safety Assessment
If you’re formulating or evaluating a suncare product with active ingredients, consider the following:
- Document the photostability of each active ingredient under typical use conditions. Photoactivation isn’t a theoretical risk if UV exposure is part of the product’s core purpose.
- Model cumulative exposure and safety margin calculations across the product lifecycle assuming realistic usage patterns and reapplication requirements.
- Be aware of any UV filters that have been subject to regulatory scrutiny and understand if data regulators are requesting additional data.
- Consider conducting phototoxicity and photosensitisation testing for formulations containing multiple actives that will be used in direct sunlight.
At XCellR8, we can support suncare-as-skincare formulation testing through human-relevant in vitro assays. We can evaluate local effects including phototoxicity, skin irritation and sensitisation potential under conditions that reflect realistic use. Additionally, we can support further skincare claims such as antioxidant activity, collagen boosting and barrier integrity. If you’re developing or evaluating a suncare-as-skincare product and need independent data to inform your safety assessment, get in touch.
Email info@x-cellr8.com or call +44 (0)1925 607 134.
References
Alcaraz, A., et al. (2024). The dual challenge of FDA-evaluated non-GRASE UV filters: Photostability and systemic absorption. A path toward safer and more effective sunscreens. European Journal of Pharmaceutics and Biopharmaceutics, 201, 114362. https://doi.org/10.1016/j.ejpb.2024.114362
European Commission. (2025). Assessment of Octinoxate (2-Ethoxyethyl p-methoxycinnamate). Scientific opinion following review under REACH regulation. Retrieved from ECHA database.
FDA. (2020). Sunscreen Drug Products for Over-the-Counter Human Use. Maximum Usage Trial data from pharmacokinetic studies of avobenzone, octocrylene, oxybenzone and ecamsule.
Matta MK, Florian J, Zusterzeel R, et al. Effect of sunscreen application on plasma concentration of sunscreen active ingredients: a randomized clinical trial. JAMA. 2020;323(3):256-267. doi:10.1001/jama.2019.20747
Grassroots Health. (2026). Balancing Sun Safety with Vitamin D Production. [Retrieved from GrassrootsHealth.net]
EWG. (2025). The Trouble with Ingredients in Sunscreen. Updated report on chemical filter absorption and regulatory status.
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