Randomised Controlled Trial of an Antioxidant and Sunscreen Combination Cream for Reducing DNA Damage in Human Skin

Overview

This randomized, double-blind, vehicle-controlled clinical trial investigates whether daily use of an encapsulated SPF 50 formulation containing a multi-antioxidant complex provides greater mitochondrial DNA (mtDNA) protection in human facial skin compared with a vehicle-only cream. Fifty-two healthy adults will be enrolled during the UK spring and randomized 1:1 to receive either the antioxidant-enriched SPF 50 or a matched vehicle (no SPF, no antioxidants). Participants will apply their assigned product once daily to the full face for 12 weeks under ambient ultraviolet (UV) and oxidative exposure. Non-invasive cheek swabs collected at baseline and week 12 will be analyzed by blinded quantitative polymerase chain reaction (qPCR) to assess mtDNA integrity (ΔCt = Ct\_long - Ct\_short). The primary objective is to determine whether the antioxidant-enriched SPF 50 reduces mtDNA damage compared with vehicle. Secondary objectives include comparing the proportion of "responders" showing reduced mtDNA damage (ΔCt \< 0) and evaluating within-participant change among habitual daily sunscreen users. The trial aims to clarify whether adding antioxidants to high-SPF formulations can strengthen daily photoprotection by mitigating residual oxidative stress not fully blocked by UV filters alone.

Chronic sun exposure generates oxidative stress that damages both nuclear and mitochondrial DNA in skin cells, contributing to photoaging. Mitochondrial DNA is particularly susceptible to ultraviolet- and reactive-oxygen-mediated injury. Even high-SPF sunscreens only partially prevent oxidative stress from UVA, visible, and infrared wavelengths. Combining topical antioxidants with UV filters may enhance cellular protection, but direct in-vivo evidence of mitochondrial benefit during daily use remains limited. This single-center, randomized, double-blind, vehicle-controlled study will evaluate the effect of a multi-antioxidant, encapsulated SPF 50 formulation on facial mitochondrial DNA integrity during twelve weeks of normal daily use. The study will be conducted during the UK spring to minimize environmental variability in ultraviolet intensity, temperature, and humidity. Healthy adults aged eighteen to seventy years with intact facial skin will be eligible regardless of baseline sunscreen habits. Individuals with active facial dermatologic disease, recent laser or peel procedures within three months, recent use of retinoids, antioxidants, or anti-inflammatory agents within four weeks, pregnancy, lactation, acute illness, or planned high-UV travel will be excluded. Participants taking medications known to affect mitochondrial function must be on stable doses for at least three months before and throughout the study. Participants will be randomized in a one-to-one ratio to receive either an encapsulated SPF 50 plus multi-antioxidant complex or a vehicle-only cream containing no SPF and no antioxidants. A small non-randomized comparator group may continue their existing skincare routine to contextualize background variability. Study products will be visually identical, coded, and packaged in identical containers to maintain blinding of participants, investigators, and laboratory staff. Each participant will apply the assigned product once daily to the entire face at a standardized dose of approximately two milligrams per square centimeter for twelve weeks. Adherence will be encouraged through written instructions and monitored by self-report and returned product weight. At baseline and week twelve, a defined two-by-two-centimeter cheek area will be sampled using a sterile synthetic-tipped swab. Samples will be labeled with coded identifiers and analyzed by a blinded external laboratory using a validated long- and short-amplicon quantitative polymerase chain reaction assay. The mitochondrial DNA integrity index, calculated as ΔCt = Ct\_long - Ct\_short, reflects lesion frequency, where a negative change indicates improved integrity. The primary outcome is the change in ΔCt from baseline to week twelve between treatment arms. Secondary outcomes include the proportion of participants with ΔCt \< 0, the within-participant change among habitual daily sunscreen users compared with their prior routine, and overall safety and tolerability of both products. Efficacy analyses will include all randomized participants with valid paired baseline and week-twelve data. Between-group comparisons will be performed using two-sided parametric and non-parametric tests, and responder proportions will be compared using Fisher's exact test at a significance level of 0.05. This study will determine whether daily application of an encapsulated SPF 50 formulation containing multiple antioxidants provides superior mitochondrial protection in facial skin compared with vehicle alone, thereby supporting the concept that antioxidant-enriched sunscreens can enhance photoprotection and reduce oxidative stress encountered in everyday life.