Fig. 1

Study design, volunteer distribution, and PCA according to skin phototype. [a] Schematic representation of the study design: 32 female volunteers received three treatments over three consecutive days: untreated control, UV exposure at 0.9 MED, and UV exposure at 0.9 MED after pretreatment with SPF 30, [b] Participant distribution across Fitzpatrick phototypes I–IV, [c] PCA of normalized gene expression by treatment (control, green; SPF 30 + UV, purple; UV, orange), shown separately by phototype. From left to right: phototypes I&II, III, and IV, illustrating phototype‑dependent clustering and treatment separation.