## 3 Results  
The most popular anti-aging treatments contain antioxidants which can act directly by restoring the physiological radical balance and/or indirectly by preventing the photoaging process. Vitamins and phenols are some of the most representative examples of cosmetic active ingredients used for anti-aging purposes. They can be used both as purecomponents or by carefully selecting precious vegetable oils characterized by a relevant and rich antioxidant unsaponifiable fraction. According to their composition (Table 1), EVOO, SAO, AKO, and JO certainly possess several compounds which could be responsible for their antioxidant properties and oxidative stability [16; 17; 23; 24]. Despite their extreme variability in composition, depending on the cultivars, the harvest time, and also on the analytical methods employed [25], these characteristics make them widely used vegetable oils of cosmetic interest. Consequently, samples were examined in terms of free radical production via the EPR spin trapping technique using PBN coupled with thermal treatment at 70 \({}^{\circ}\)C.  
Firstly, the EPR spectra of each oil (not irradiated or irradiated for different periods of time) were acquired following the treatment with a fixed amount of PBN but a different period of thermal treatment (70 \({}^{\circ}\)C). As an example, Figure 1 shows the EPR spectra of the stable PBN spin adducts formed in the EVOO sample after 30 min of incubation at 70 \({}^{\circ}\)C with the not-irradiated sample and UV-irradiated ones (30, 60, and 120 min). As is observable, the intensity of the EPR signal increases together with the UV irradiation time. This increase is indicative of PBN spin adducts' accumulation, corresponding to greater free radical production. Similar results have been obtained for the other analyzed oils. Clearly, the PBN-adducts formation measurable via EPR spectroscopy is strictly connected to the formation of free radicals caused by the UV irradiation treatment and/or the following thermal incubation period. This phenomenon was then monitored by measuring the peak-to-peak amplitude (H\({}_{\text{P/P}}\)) between the EPR signals of the PBN-adduct (as shown in Figure 1) every 5 min of thermal treatment at 70 \({}^{\circ}\)C. It should be noted that, also immediately after irradiation, the signal was not equal to 0. Indeed, the ratio of the EPR signal of all oils after UV irradiation vs. unirradiated is in the range 1.5-12. To compare and analyze the enormous set of obtained data, the calculated H\({}_{\text{P/P}}\) values were plotted against time to highlight the accumulation of free radicals. Furthermore, according to several studies aimed at predicting the oxidative stability of oils [21; 22; 26], the obtained graphs were used to determine both the induction time and the slope of the linear portion. The induction time (IT), also called the induction period (IP) or lag-time, corresponds to the range of time during which radicals are formed very slowly before a sudden sharp linear appears. It is, therefore, an index of the oxidative stability of each sample, and it is equal to the projection on the x axis of the point of intersection between the tangents to the two portions of the