Sun oils: effect of the applied dose on SPF determined by using in vitro method

Area of Science:

• Dermatology
• Photoprotection
• Cosmetic Science

Background:

• Established link between sun exposure and skin cancer necessitates effective sun protection.
• Sun Protection Factor (SPF) quantifies sunscreen efficacy using in vivo or in vitro methods.
• Consumer awareness regarding proper sunscreen application is crucial for adequate photoprotection.

Purpose of the Study:

• To investigate the impact of reduced sunscreen application on actual sun protection factor (SPF).
• To determine the level of protection achieved when consumers apply half or a quarter of the recommended sunscreen dose.
• To analyze the variability in SPF reduction across different sunscreen products under sub-optimal application.

Main Methods:

• Utilized an in vitro method for ethical reasons, adhering to standard protocols.
• Tested 20 commercially available sunscreen oils across five different application doses (5–15 mg/25 cm²).
• Quantified the relationship between applied product mass and resulting SPF using polynomial functions.

Main Results:

• A polynomial function describes the relationship between SPF and the mass of sunscreen applied.
• Reducing the applied sunscreen dose by half significantly decreases efficacy, with SPF reduction factors ranging from 2 to 4.
• The degree of efficacy reduction varies considerably among different sunscreen formulations.

Conclusions:

• Current recommended sunscreen application amounts are critical for achieving labeled SPF.
• Consumers applying sub-therapeutic doses of sunscreen receive substantially less protection than indicated by the SPF value.
• Further consumer education on correct application is vital to ensure effective sun protection and reduce skin cancer risk.