Sunscreen Efficacy and SPF Testing

Sunscreen products are “any preparation (such as creams, oils, gels, sprays) intended to be placed in contact with the human skin with a view exclusively or mainly to protecting it from UV radiation by absorbing, scattering or reflecting radiation” and they fall within the scope of the EU Cosmetics Regulation. To ensure sunscreen products’ safety and efficacy, regulatory frameworks worldwide, including the European Union (EU), require comprehensive testing to substantiate claims such as Sun Protection Factor (SPF), PA (Protection Grade of UVA), and water resistance.

To ensure consumer safety and claim validity for sun products, the following standards and guidelines are critical:

• EN ISO 24442:2011 – Sun protection test methods – In vivo determination of sunscreen UVA protection;
• EN ISO 2443:2021 – Determination of sunscreen UVA photoprotection in vitro;
• EN ISO 24444:2020 – Sun protection test methods – In vivo determination of the sun protection factor (SPF).

 

SPF Testing: Substantiating UVB Protection

SPF, a measure of protection against UVB rays, is one of the most important claims on sunscreen labels. Testing to substantiate SPF values is performed according to ISO 24444:2019, which specifies the in vivo method.

Sunscreen products cannot filter all UV radiations, but they have to protect against both UVA and UVB. According to the EU Commission Recommendation of September 22, 2006 on the efficacy of sunscreen products and the claims made relating thereto, minimum degrees of protection to consider a sunscreen effective are:

• Sun protection factor (SPF) 6 against UVB;
• UVA protection factor of 1/3 of the sun protection factor;
• A critical wavelength of 370 nm.

Products that do not meet the above criteria cannot be marketed as sunscreen products.

The variety of numbers used on labels for indicating the SPF should be restricted in order to facilitate the comparison between different products without reducing the choice for the consumer. The following range of sun protection factors for each category and the respective labelling is recommended:

UVA Protection and PA Claims

UVA protection is essential to complement UVB protection, as UVA rays penetrate deeper into the skin and contribute to long-term damage. In the EU, compliance with the UVA protection factor (UVA-PF) is mandatory.

• ISO 24442:2023: This standard describes the in vivo method for determining UVA-PF.
• UVA/UVB Ratio: The EU requires that UVA protection be at least one-third of the SPF value.
• PA (Protection Grade of UVA): Originating in Asia, the PA system uses “PA+” ratings based on persistent pigment darkening (PPD) testing, which may also align with ISO 24442 methods.

Water Resistance Testing

Sunscreens often claim water resistance, indicating their effectiveness even after water exposure. Testing for these claims follows ISO 18861:2022.

Methodology:

In Vivo Testing:

1. Participants undergo water immersion for a specified time (e.g., 40 or 80 minutes).
2. SPF is measured before and after immersion to assess retention of efficacy.

Claim Standards:

• “Water-resistant” indicates ≥50% of SPF is retained after water exposure.
• “Very water-resistant” requires retention after two consecutive water immersions.

 

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SPF Laboratory Test – Sun Protection Factor