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.

Inclusion Criteria:

• Adults aged 18-80 years
• Healthy facial skin with no active dermatologic disease
• Willing to apply the assigned product daily for 12 weeks
• Willing to avoid additional facial skincare products during the study period
• Able to attend baseline and week-12 visits for cheek-swab collection
• Willing to maintain stable medication and supplement use throughout the study
• Provided written informed consent

Exclusion Criteria:

• Active facial dermatologic disease or visible facial skin lesions
• Laser, peel, or energy-based facial treatment within the past 3 months
• Use of topical/systemic retinoids, antioxidants, or anti-inflammatory agents within 4 weeks of baseline
• Pregnancy or breastfeeding
• Recent acute illness or infection
• Planned travel to high-UV or sunny destinations during the study period
• Current smoker or regular e-cigarette user
• Participation in another clinical trial within the previous 30 days
• Known allergy or sensitivity to study-product ingredients
• Unstable medical conditions or medications known to affect mitochondrial function (e.g., recent changes in antibiotics, statins, or thyroid medication)

Deidentified individual participant data will be shared, including mtDNA ΔCt values (baseline and week 12), treatment assignment, age, and habitual sunscreen-use category. Questionnaire outcome data and adverse event information will also be available. The shared dataset will exclude all direct identifiers and any genomic sequence data beyond ΔCt metrics.

Available within 12 months after primary completion and for 36 months thereafter.

Access will be granted upon reasonable written request accompanied by a brief proposal and analysis plan. Requests will be reviewed by the study steering team, and ethics approval or exemption may be required depending on local regulations.

This is a double-blind study with multiple levels of masking. Participants, care providers, investigators, and outcome assessors are blinded to treatment allocation. Study creams are dispensed in identical, opaque containers labeled only as "Formulation A" or "Formulation B." The randomization code is maintained by an independent administrator who is not involved in participant interaction, data collection, or analysis. Laboratory personnel and statisticians receive only anonymized, coded samples and datasets. Unblinding will occur only after database lock and completion of all primary analyses.