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Background Skin is affected by environmental stress such as ultraviolet exposure. Topically applied antioxidants confer protection against this stress. Spinach thylakoid extracts are plant samples known as photosynthetic membranes containing antioxidant molecules able to dissipate excess of energy and oxidative stress. Methods Antioxidant contents and activities were tested in thylakoid extracts stored for different periods at 4°C to compare their efficacities. Cytotoxicity of thylakoids was tested on human THP‐1 cells along with the capacity to protect from oxidative stress using flow cytometry. Protection of thylakoids against ultraviolet was tested on engineered human skin using two formulations and evaluated by electronic microscopy. Results Results indicate that thylakoid extracts possess antioxidant molecules that were not significantly affected by storage at 4°C whereas photosynthetic activity was storage‐dependent. Thylakoid extracts were not cytotoxic to human THP‐1 cells, and three extracts protected cells against reactive oxygen species. Moreover, formulation comprising 0.1% or 0.01% of thylakoids and sunscreen provided a synergetic protection against UV exposure. Thylakoid extracts mixed with a neutral cream were also able to repair UV damages on engineered human skin. Conclusions Thylakoid extracts contained various antioxidant molecules, and their properties were maintained in over storage at 4°C for more than 72 months. Molecules and enzymes present in thylakoid extracts are involved in protecting and restoring the harmful effects of UV exposure. The involvement of antioxidant molecules such as carotenoids, SOD, and Fe‐S clusters in cellular and regulatory metabolic reactions may explain the observed protective effects.

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