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New active ingredients, including those of plant origin, which could protect the skin against various harmful factors, such as UV radiation and free radicals responsible for skin ageing, are still being sought. The present study was focused on the antioxidant activity of Hippophaë rhamnoides L. and Vaccinium oxycoccos L. fruit glycolic extracts. Investigations were also carried out to evaluate the effect of UVA radiation and the storage of the sea buckthorn and European cranberry extracts at an elevated temperature of 50 °C on their interactions with free radicals. The kinetics of the interactions of the extracts with DPPH were assessed using electron paramagnetic resonance (EPR) spectroscopy. The sea buckthorn and European cranberry extracts quench the EPR signal of DPPH free radicals, which indicates their antioxidant potential. The EPR method further showed that a mixture of sea buckthorn and cranberry extracts in a volume ratio of 2:1 was more potent in quenching free radicals compared to a mixture of these extracts in a ratio of 1:2. Our findings demonstrate that long-term UVA radiation exposure reduces the ability of sea buckthorn and cranberry extracts to interact with free radicals. Moreover, storage at elevated temperatures does not affect the interaction of sea buckthorn extract with free radicals, while it alters the ability of cranberry extract to interact with free radicals. This study has demonstrated that an important factor in maintaining the ability to scavenge radicals is the storage of raw materials under appropriate conditions. H. rhamnoides and V. oxycoccos extracts can be used as valuable raw materials with antioxidant properties in the pharmaceutical and cosmetic industries. [ABSTRACT FROM AUTHOR]