With the arrival of the season of greater sun exposure, sunscreen products once again take centre stage both in the market and in the technical evaluation of cosmetic products. In this category, formulation alone is not enough. A sunscreen must demonstrate, through appropriate testing and recognised methods, that the protection declared on its label corresponds to its actual performance on the skin. The ISO standards applicable to sunscreens were developed precisely to harmonise this evaluation and make results comparable and technically consistent.
In recent years, sunscreen evaluation has continued to evolve. The sector is incorporating new standards and technical approaches for SPF determination, in line with a trend towards more precise, more standardised and technically stronger methods. This evolution reinforces the importance of ensuring that manufacturers and brands do not simply formulate the product, but also properly plan their testing and validation strategy.
Why sunscreen products require specific evaluation
Unlike other cosmetics, a sunscreen is directly related to protection against UV radiation. For this reason, its evaluation must consider not only the composition of the product, but also its actual efficacy and the consistency between that efficacy and the claims used.
Among the aspects that normally need to be verified in a sunscreen are:
- the declared SPF;
- UVA protection;
- the correct application of the test method;
- the consistency of the product between formulation, testing and labelling;
- and, where relevant, the suitability of the product for newer instrumental or in vitro methodologies.
To better understand how this evaluation is structured, it can be summarised in the following technical blocks:
| Aspect evaluated | What it measures | Usual method | What it provides |
| SPF | Protection against erythema induced by UVB and part of the UV spectrum | ISO 24444 | Allows the declared sun protection factor to be determined |
| UVA protection | Level of protection in the UVA range | ISO 24442 | Allows the product’s specific UVA protection to be assessed |
| UV/UVA source control | Quality and stability of the radiation used in the test | Requirements defined in ISO 24444 and ISO 24442 | Guarantees the technical validity of the study |
| Analytical control of the formulation | Verification of relevant components and product consistency | Analytical techniques such as HPLC, depending on the type of study | Strengthens quality control and formulation consistency |
Procedure (Specific Section: Evaluation of Product Homogeneity)
Prior to conducting any efficacy testing on sunscreen products, the homogeneity of the product must be verified, especially in formulations containing mineral filters (e.g., zinc oxide or titanium dioxide).
Homogeneity is defined as the uniform distribution of active ingredients within the product matrix, ensuring that each application provides equivalent protection. This aspect is critical because:
- Mineral filters have a natural tendency to sediment or aggregate.
- Lack of homogeneity may lead to:
- Decreased photoprotective efficacy.
- Variability in SPF/UVA test results.
- Reduced product shelf life.
- Risks associated with non-uniform protection for the end user.
Homogeneity Evaluation
Homogeneity shall be assessed using appropriate analytical techniques that allow determination of filter distribution within the product, both under initial conditions and after stability studies.
The use of advanced techniques such as X-ray Fluorescence (XRF) is recommended, as it allows:
- Analysis of mineral filter distribution without complex sample preparation.
- Detection of sedimentation or phase separation phenomena.
- Evaluation of intra-batch and inter-batch uniformity.
The XRF equipment must be qualified and calibrated in accordance with internal quality control procedures.
For further information on the application of this technique in cosmetics and pharmaceuticals, refer to the following technical resource: https://shapypro.com/s2-puma-analysis-cosmetics-pharma/
Acceptance Criteria
The product shall be considered homogeneous when:
- Variability in mineral filter concentration across different sample points is within the limits established in internal specifications.
- No visible or measurable sedimentation phenomena are observed after stress or storage conditions.
- Analytical results are consistent and reproducible.
If homogeneity criteria are not met, the product shall not undergo efficacy testing until the formulation or manufacturing process has been corrected
Efficacy Testing for Sunscreen Products: SPF and UVB Protection
ISO 24444 specifies the in vivo method for determining the sun protection factor (SPF) in products that absorb, reflect or scatter UV radiation and are intended to come into contact with human skin. The standard explains that SPF is calculated from the relationship between the minimum erythemal dose on protected and unprotected skin, using a solar simulator and human volunteers.
This means that SPF is not simply a laboratory estimate, but the result of a regulated procedure that includes:
- selection of test subjects;
- definition of application areas on the back;
- controlled application of the product;
- exposure to UV radiation under defined conditions;
- visual evaluation of the erythemal response;
- and statistical treatment of the results.
The standard also establishes that the product must be applied at 2.00 mg/cm² ± 0.05 mg/cm², since the amount applied and the uniformity of distribution directly influence the magnitude and variability of the result.
UVA Protection Testing for Sunscreen Products
One of the most important points in sunscreen products is that a high SPF does not by itself guarantee sufficient or balanced UVA protection. ISO 24442 makes this clear in its introduction: a product may show a high SPF and still provide only modest UVA protection. For this reason, assessment of the UVA range requires a specific method.
ISO 24442 establishes an in vivo method for determining the UVA protection factor (UVA-PF) through the evaluation of persistent pigment darkening (PPD). In this procedure, the minimum UVA dose required to induce persistent pigmentation in protected and unprotected skin is compared, again on human volunteers and under controlled conditions.
This test is especially important in seasonal products such as:
- facial sunscreens;
- high-protection body sunscreens;
- children’s products;
- sticks and specific formats for sensitive areas;
- and daily photoprotection products seeking more balanced protection across the full UV spectrum.
Control of the radiation source and test conditions
The quality of the study also depends on the quality of the irradiation system. Both ISO 24444 and ISO 24442 detail requirements for the radiation source, its spectrum, beam uniformity, and radiometric and spectroradiometric control.
For SPF, ISO 24444 requires a UV source with a continuous spectrum, without extreme emission peaks, and with appropriate proportions of UVA II and UVA I within the total spectrum. It also states that total irradiance must not exceed 1,600 W/m² and recommends full spectroradiometric verifications at least every 18 months or after 3,000 operating hours of the lamp.
For UVA-PF, ISO 24442 requires a solar simulator with a xenon arc lamp, control of UVB content, a defined distribution between UVA I and UVA II, and specific limits for visible and near-infrared radiation. It also stresses the need for periodic spectroradiometric control and that the use of filters alone does not guarantee correct emission.
Subject selection and statistical validity of the study
Another key point is that these tests are not based solely on observing a skin response, but also on clearly defined methodological and statistical criteria.
For SPF testing, ISO 24444 establishes that subjects must belong to phototypes I, II or III, or show an ITA value above 28°, and that at least 10 valid results must be obtained, with a maximum of 20, while meeting a 95% confidence interval within ±17% of the measured mean SPF. If that criterion is not met, the number of subjects must be gradually increased, and if it is still not met after 20 valid results, the test is rejected.
For UVA, ISO 24442 follows a similar logic: at least 10 valid UVA-PFi values are required, with a maximum of 20 valid results, and the 95% confidence interval must also remain within ±17% of the mean value. If not, the complete test must be repeated.
Reference formulations and validation of the study
Both standards also include the use of reference sunscreen formulations, which is essential to validate that the procedure is being carried out correctly.
For SPF, ISO 24444 includes reference formulations P2, P3 and P7, with defined mean values and acceptance limits. If the reference sunscreen does not behave within those limits, the entire study must be rejected.
For UVA, ISO 24442 uses formulations S1 and S2 to control the reliability of the study, with expected acceptance ranges for UVA-PF. If the result for the reference product does not fall within the expected interval, the test is not valid.
Analytical control of sunscreen products
In addition to efficacy studies, sunscreen products require good analytical control of their composition. The standards themselves include HPLC procedures in the reference formulations to verify relevant analytes and acceptance criteria such as coefficients of variation and recovery.
ISO 24444 includes analytical procedures associated with reference formulations P2, P3 and P7 to verify active ingredients by HPLC and assess control compliance.
ISO 24442 does the same for formulations S1 and S2, including sample preparation conditions, chromatography, calculation and acceptance criteria.
This point is important because in sunscreens it is not enough to measure final efficacy alone. It is also advisable to ensure that the product is properly formulated, that the filter content is consistent with the formulation design, and that analytical characterisation supports both development and quality control of the finished product.
New ISO standards and the evolution of evaluation methods
The evaluation of sunscreen efficacy continues to move towards increasingly refined and updated methods. Alongside the classic in vivo tests for SPF and UVA protection, the sector’s technical framework is incorporating new standards aimed at improving the characterisation of photoprotection and strengthening the robustness of the data obtained. For manufacturers and brands, this means paying attention not only to traditional requirements, but also to the evolution of the technical criteria applicable to product validation.
This change confirms a clear trend in the industry: complementing established methods with more refined procedures and new evaluation tools. In practice, this translates into a growing need to integrate formulation development, analytical control, efficacy testing and documentary review into a single technical strategy, rather than treating each phase as if it had nothing to do with the next.
How SHAPYPRO can help
In this context, SHAPYPRO can help manufacturers and brands structure the technical evaluation of their sunscreen products, reviewing which efficacy studies and analytical controls are necessary depending on the formulation, the type of product and the intended claims. In addition, within the framework of analytical control, it can provide complementary instrumental support through techniques such as those described in its article on the S2 PUMA, especially in applications related to the characterisation and control of raw materials or mineral filters.
Conclusion
Sunscreen products require a solid technical evaluation. SPF and UVA protection must be demonstrated through standardised methods, supported by appropriate control of the test procedure and product composition.
During the sunscreen season, this is especially important. A sunscreen should not merely promise protection, but be able to demonstrate it with reliable data and a coherent technical strategy from development through to final labelling.