Sunscreen ISO standards:
what each one measures and how

In March 2025, Thailand's Consumer Council and Chaladsue magazine published SPF test results for many sunscreen brands and found several whose SPF and PA did not match their labels, measured against the Thai Cosmetics Committee notification on displaying sun protection values (2017).

Since then many consumers ask whether a sunscreen is "ISO tested" and by which method. For brand owners, understanding these standards builds credibility and helps answer customers.

• SPF (Sun Protection Factor) measures protection against UVB, the main cause of sunburn. It compares the UV dose that reddens protected skin with the dose that reddens unprotected skin; SPF 30 means about 30 times more UV is needed before redness appears.
• PA (Protection Grade of UVA) shows protection against UVA, which reaches deeper and is linked to dullness and wrinkles. It runs from PA+ to PA++++; more plus signs mean higher UVA protection.

SPF and PA come from different tests, so a complete protection claim needs both.

ISO 24444:2019 — SPF on volunteers (in vivo)

A set amount of sunscreen is applied to volunteers' backs, which are exposed to several doses from a solar simulator. Technicians then read the dose at which skin starts to redden (MED). SPF is the ratio of MED on protected skin to MED on unprotected skin. It has been the reference method for decades, but volunteers must be exposed until their skin reddens.

ISO 23675:2024 — SPF in the lab (Double Plate, in vitro)

A robot spreads sunscreen on two kinds of PMMA plate, sandblasted and moulded, to mimic the skin surface. A spectrophotometer measures UV transmission before and after irradiation to calculate SPF, with no volunteers. Published in December 2024, it applies to emulsions and single-phase alcoholic products, not powders or sticks, and not to water resistance.

ISO 23698:2024 — HDRS (Hybrid Diffuse Reflectance Spectroscopy)

A hybrid method combining an absorbance spectrum measured on plates with diffuse reflectance measured on volunteers' skin at low, non-burning doses. One test gives three results: SPF, UVA-PF and critical wavelength. Published in December 2024.

ISO 24442:2022 — UVA protection on skin (in vivo)

Protected and unprotected skin is exposed to UVA, and persistent pigment darkening (PPD) is measured. The result underpins the PA grade.

ISO 24443:2021 — UVA protection and critical wavelength in the lab (in vitro)

UV transmission through a sunscreen film on PMMA plates is used to calculate UVA-PF and critical wavelength (the wavelength below which 90% of UV absorbance lies). It supports broad-spectrum claims; a common criterion is a critical wavelength of at least 370 nm, and in the EU UVA-PF must be at least one third of SPF.

ISO 16217:2020 and ISO 18861:2020 — water resistance

ISO 16217 sets the water immersion procedure; ISO 18861 sets how to calculate the percentage of SPF retained after immersion. Together they support a water-resistant label claim.

• Start with your target market. Accepted methods differ by country; in Thailand, SPF and PA labelling must follow the Cosmetics Committee notification.
• New methods do not replace old ones overnight. In Europe, Cosmetics Europe recommends giving preference to ISO 23675 and ISO 23698, while existing ISO 24444 results remain valid. Many companies use ISO 23675 during development and in vivo testing for final substantiation where regulators require it.
• Test the final formula at an accredited laboratory and keep the report on file whenever you communicate SPF and PA.
• Don't confuse it with ISO 22716, which certifies the factory's manufacturing system, not sun protection. A trustworthy sunscreen has both an ISO 22716 factory and sun protection results from a suitable standard.

Mark Bio is an ISO 22716 and GMP certified cosmetics factory. Our cosmetic R&D team develops formulas to your brief and plans sun protection testing to suit your target market, handling formula, samples, Thai FDA notification, packaging, production and delivery. Minimum order starts at 5,000 units per formula.