Evidence for beneficial effects of squalene on ultraviolet (UV)-induced photoageing of the skin is lacking. Aim. To investigate whether squalene supplementation improves signs and molecular markers of photoageing in human skin in vivo. Methods. In total, 40 female volunteers aged > 50 years received two different doses [13.5 g/day (low-dose group) and 27 g/day (high-dose group)] of squalene for 90 days. At baseline and at the completion of the study, facial wrinkles were measured using skin replicas. Skin samples were taken to compare type I procollagen and matrix metalloproteinase 1 mRNA levels by real-time reverse-transcriptase PCR, and for type I procollagen immunostaining. Skin samples were also taken 24 h after 2 × minimal erythema dose (MED) of UV irradiation before and after squalene intake to assess UV-induced thymine dimer formation and keratinocytic apoptosis. Results. In total, 37 subjects completed the trial. Transient loose stool was experienced by 35% of volunteers in the low-dose group and 55% in the high-dose group. Facial wrinkles decreased significantly (P < 0.05) in the high-dose group, while procollagen type I mRNA levels and MED increased significantly in the low-dose group. Procollagen immunostaining tended to increase in both groups. Facial erythema decreased and pigmentation increased significantly in both groups. UV-induced keratinocytic apoptosis and thymine dimer staining were substantially reduced in both groups. Conclusions. Daily ingestion of 13.5 or 27 g of squalene per day resulted in antiageing effects in photoaged skin. However, in view of the frequent incidence of loose stool experienced by the subjects, the risk-benefit ratio of high-dose squalene supplementation is too high to recommend it for treating skin ageing.