ISO 24444:2019— In Vivo Determination of SPF

The introduction of an SPF (Sun Protection Factor) began in the 1930s. Austrian chemist Franz Greiter, inspired by a sunburn while climbing a mountain, developed Gletscher Crème— one of the first effective sunscreens. The SPF rating system, a global standard for measuring UVB protection, was introduced in the 1960s by Greiter. Today, SPF is crucial for choosing effective sunscreen as it indicates how well a product protects against UVB rays. ISO 24444:2019—Cosmetics – Sun protection test methods – In vivo determination of the sun protection factor (SPF) provides a basis for the evaluation of sunscreen products for the protection of human skin against erythema induced by solar ultraviolet rays (commonly known as sunburn).

What Is Vivo SPF Determination?

The Sun Protection Factor (SPF) indicates how long a sunscreen can protect skin from UVB radiation before it would start to burn, compared to unprotected skin. UVB rays are the primary cause of sunburn and some skin cancers. In vivo SPF determination measures a sunscreen’s protection by comparing the time it takes for skin to redden (erythema) with and without the sunscreen applied, using a standard protocol outlined by organizations like ISO. 

This method involves exposing volunteers’ skin to UV radiation, both with and without the sunscreen applied, and then observing the time it takes for erythema (redness) to appear. In vivo SPF determination is crucial for accurately assessing sunscreen efficacy and assuring reliable consumer labeling. ISO 24444:2019 details the test method requirements.

What Is ISO 24444?

ISO 24444:2019 specifies a method for the in vivo determination of the sun protection factor (SPF) of sunscreen products. The international standard is applicable to products that contain any component able to absorb, reflect or scatter ultraviolet (UV) rays that are intended to be placed in contact with human skin.

ISO 24444:2019/Amd1:2022 contains slight provisions to the text of ISO 24444:2019.

What Is the SPF Test Method in ISO 24444?

The SPF test method in ISO 24444:2019 is a laboratory method. This test utilizes a xenon arc lamp solar simulator (or equivalent) of defined and known output to determine the protection provided by sunscreen products on human skin against erythema induced by solar ultraviolet rays. To conduct the test, a section of each human subject’s skin is exposed to ultraviolet light without any protection while another (different) section is exposed after application of the sunscreen product under test.

To determine the sun protection factor, ISO 24444:2019 details that incremental series of delayed erythemal responses are induced on a number of small sub-sites on the skin. These responses are visually assessed for presence of erythema 16 to 24 hours after UV radiation, by the judgment of a trained and competent evaluator.

What Are the Key Aspects of In Vivo SPF Testing?

• Volunteers: A minimum of 10 volunteers are typically used for the test.
• Sunscreen Application: A specific amount of sunscreen is applied to the protected skin.
• Erythema Observation: The time it takes for erythema to appear is carefully monitored.
• Skin Exposure: Small areas of skin on the volunteers are exposed to UV radiation. 

ISO 24444:2019—Cosmetics – Sun protection test methods – In vivo determination of the sun protection factor (SPF) is available on the ANSI Webstore.