The detrimental effects of solar radiation on the skin are well-established, with ultraviolet (UV) radiation long being the primary focus of sun protection strategies. However, recent scientific evidence indicates that infrared (IR) radiation also contributes significantly to skin photoaging, increases the risk of carcinogenesis, and can lead to the degradation of protective carotenoids, disruption of calcium homeostasis, and activation of apoptosis pathways. These biological effects are mediated by increased reactive oxygen species and the heightened expression of metalloproteinases in the skin. Traditional sunscreen products are primarily designed to protect against UV radiation by absorbing, scattering, or reflecting UV photons, often leaving the skin vulnerable to the harmful effects of other parts of the solar spectrum, including IR. To address this gap in photoprotection, this study investigates the potential of cold-pressed plant oils as photoprotective agents in the infrared spectral range, leveraging their known ability to strengthen the skin barrier and exhibit various beneficial properties like antioxidant and anti-inflammatory effects.
Methods
This in vivo study evaluated ten cold-pressed plant oils by measuring the directional–hemispherical reflectance (DHR) of the skin of 12 volunteers (phototypes I-III) in the infrared range (1000–2500 nm). Measurements were taken on the forearms before (S), immediately after (T1), and 30 min after (T2) the topical application of the oils. The study also analyzed the correlation between the oils’ content of chlorophyll a, chlorophyll b, lycopene, and β-carotene, their antioxidant activity (DPPH assay), and the observed changes in skin DHR.
Key Findings
•A statistically significant increase in the skin’s reflectance in the 1700–2500 nm range was observed 30 minutes after the application of chokeberry, fig, pomegranate, and perilla oils, suggesting their potential as photoprotective agents against IR radiation. The percentage increases were 3.9% for chokeberry, 7.0% for fig, 5.3% for pomegranate, and 11.2% for perilla oil.
•In the spectral range of 1000–1700 nm, the median skin reflectance immediately after oil application (T1) was statistically significantly lower for elderberry, blackcurrant, fenugreek, poppy, and carrot oils compared to before application (S).
•A statistically significant negative correlation was found between the chlorophyll a content of the oils and the immediate decrease in skin reflectance (T1-S) in the 1000–1700 nm range. Higher chlorophyll a content led to a greater decrease in reflectance.
•In the 1700–2500 nm range, a statistically significant negative correlation was observed between the lycopene content of the oils and the decrease in reflectance both immediately after (T1-S) and 30 minutes after (T2-S) application. Higher lycopene content corresponded to a lower reflectance.
•No statistically significant correlations were found between β-carotene content or the antioxidant potential of the oils (based on DPPH assay) and changes in skin reflectance in either of the IR spectral ranges analyzed.
Researchers offers novel insights into the infrared photoprotective properties of specific cold-pressed plant oils. The finding that chokeberry, fig, pomegranate, and perilla oils significantly increased skin reflectance in the 1700–2500 nm range after penetrating the epidermis suggests a potential mechanism for protecting the skin against the harmful effects of IR radiation, complementing traditional UV filters. The study also highlights the utility of directional–hemispherical reflectance measurements as a non-invasive in vivo method for assessing the efficacy and kinetics of cosmetic ingredients designed for IR photoprotection. Future research should focus on validating these findings in larger and more diverse populations, investigating the long-term effects of these oils, and further elucidating the specific compounds responsible for the observed photoprotective effects. Understanding these mechanisms could pave the way for the development of innovative, broad-spectrum sunscreen formulations incorporating these natural ingredients.
Link to the study: https://www.mdpi.com/2079-9284/12/2/80
