ISO 24444 Cosmetic Products - Determination of Sun Protection Factor (SPF) in Living Organisms

The "ISO 24444 Cosmetics - Sun protection test methods - Determination of sun protection factor (SPF) in living organisms" standard, developed by the International Organization for Standardization (ISO), describes a method for determining the sun protection factor (SPF) of sunscreen products in living organisms. This method applies to products containing any component that can absorb, reflect, or scatter ultraviolet (UV) rays and intended for contact with human skin.

This standard provides a basis for evaluating sunscreen products in terms of their ability to protect human skin against erythema caused by ultraviolet rays from the sun.

For the purposes of this standard, the following definitions apply:

• Ultraviolet radiation (UVR): Electromagnetic radiation in the range of 290 nm to 400 nm.
• Ultraviolet B (UVB): Electromagnetic radiation in the range of 290 nm to 320 nm.
• Ultraviolet A (UVA): Electromagnetic radiation in the range of 320 nm to 400 nm.
• Erythema effective radiation Eer: This is a radiometric quantity obtained by multiplying the spectral radiation of the solar simulator at each wavelength by the erythema effective spectrum ser(λ) Eλ and integrating it in the wavelength range between 290 nm and 400 nm.
• Erythemal effective radiation exposure, erythema dose (Her): A radiometric quantity defined as the time integral of erythemal effective radiation.

The SPF test method is a laboratory procedure that uses a solar simulator (or equivalent) with a xenon arc lamp having a defined and known output to determine the protection provided by sunscreen products against erythema caused by the sun's ultraviolet rays on human skin.

The test should be limited to the back region of selected human subjects.

In each subject, a section of skin is exposed to ultraviolet light without any protection, while another (different) section is exposed after the sunscreen being tested is applied. A third section is exposed after a reference SPF sunscreen formulation is applied, which is used to validate the procedure.

To determine sun protection factor, a series of small, progressively increasing delayed erythema responses are generated in a number of sub-areas of skin. These responses are visually assessed for the presence of erythema by a trained and competent assessor 16 to 24 hours after UV radiation exposure.

The individual minimum erythema dose for unprotected skin and the individual minimum erythema dose obtained after applying sunscreen are determined on the same subject on the same day. For each subject tested, the individual sun protection factor is calculated as the ratio of the individual minimum erythema dose on product-protected skin to the individual minimum erythema dose on unprotected skin, as in the given formula.

The sun protection factor (SPF) for the product is the arithmetic mean of all valid results obtained from each subject in the test, and is expressed to one decimal place.

In short, the ISO 24444 standard specifies an internationally accepted method for determining the sun protection factor (SPF) of sunscreen products through testing on live human subjects. This standard is considered the gold standard for SPF testing and labeling in most countries worldwide.

The primary purpose of the ISO 24444 standard is to provide a repeatable, scientifically based method for measuring how effectively a sunscreen product protects human skin against UVB-induced erythema (sunburn). The SPF value indicates the ratio of the amount of UV energy required to cause minimum redness (minimum erythema dose) on protected skin compared to unprotected skin.

Simply put, if unprotected skin burns after 10 minutes of sun exposure (SPF 30), it means the product allows for approximately 30 times longer exposure (around 300 minutes) before the same level of redness appears (assuming ideal conditions and correct application).

This standard applies to any cosmetic product that contains ingredients capable of absorbing, reflecting, or scattering UV rays, is intended for skin contact, and claims to provide sun protection.

The ISO 24444 standard method involves human volunteers and adheres to a strict protocol to ensure ethical, safe, and scientifically valid results. The basic principles of the in vivo testing method are as follows:

• Panel selection: Healthy volunteers with specific skin phototypes (typically Fitzpatrick types I-III, light to medium skin tones that burn more easily).
• Test areas: Multiple defined areas on the back are used.
• Product application: Sunscreen is applied at a precise concentration of 2 mg/cm2.
• UV exposure: Artificial sun-simulated radiation is used to expose areas to increased doses.
• Determining the minimum erythema dose: First, the unprotected minimum erythema dose is determined. The protected minimum erythema dose is determined approximately 15-30 minutes after sunscreen application on the treated areas.
• Sun protection factor (SPF) calculation: Sun protection factor = Protected minimal erythema dose / Unprotected minimal erythema dose (individual values). Then, an average is taken on at least 10 valid subjects with statistical validation (confidence interval requirements to ensure reliability).
• Controls and validation: Includes reference sunscreen standards, statistical criteria for accepting/rejecting results, and measures to minimize variability.

This method emphasizes ethical considerations (informed consent, compliance with the Helsinki Declaration, limited UV exposure to avoid serious burns) and good laboratory/clinical practices.

This standard is considered important for the following reasons:

• Consumer protection: Ensures that SPF claims on labels are accurate and globally comparable.
• Legal acceptance: Adopted by authorities in the EU, many Asian countries, Australia and other countries for sunscreen registration and labeling.
• Industry standard: Used by testing laboratories worldwide to verify sunscreen effectiveness.
• Limitations and ongoing development: The in vivo method involves intentionally inducing mild sunburn on volunteers, which raises ethical concerns and exhibits some inter-individual variability.

In short, the ISO 24444 standard continues to be the cornerstone of reliable, scientifically based SPF measurement in the cosmetics industry.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the ISO 24444 standard.