## 4 Discussion  
The aims of this review, were to attract interest in alpha-phellandrene and, in a wider context, to highlight its potential applications in the pharmaceutical and food industries. There are preliminary data concerning the potential of alpha -Phellandrene, as a pure compound, in antimuoral, antinociceptive, larvicidal and insecticidal applications. Additionally, several EOs, in which alpha-phellandrene is one of the main compounds, show promising results and represent a preliminary dataset to identify new active molecules. According to ISO 9235:2021, EOs must be described by the following extraction methods: steam distillation, dry distillation and mechanical extraction from the epicarp of citrus fruits. The present definition is useful in order to distinguish an EO from similar vegetal extracts, such as absolutes, alcoholates, concretes and oleoresins [108]. EOs are volatile and oily liquids easily distinguishable due a typical fragrance and can be obtained from a large number of plants and different anatomical parts, such as seeds, leaves, flowers, barks, fruits and roots. As reported by [PERSON] and [PERSON] [109], at the beginning of the 16 th century the concept of EOs was conceived by a Swiss scientific pioneer studying a drug called \"Quanta essentia\". Concerning the chemical composition, EOs are complex mixtures of several volatile compounds, including monoterenes, sesquiterpenes, esters, ketones, aldehydes and alcohols. Among the many EO activities, the antimicrobial activity is very interesting for its possible applications to humans, animals, and food preservation and shows relevant variability, due to the heterogeneous chemical composition of the EOs, the chemotypes, and the different conditions relating to the cultivation, harvesting and processing of plant material. As reported by several authors [110,111], EO antimicrobial activity is probably linked to damage to the cytoplasmic membrane, interference with ion exchange and others enzyme inhibitory effects and modifications in ATP levels. The aforementioned mechanisms of action interfere with the permeability of the cell membrane to such an extent that the microorganism dies. In the present review article, alpha-phellandrene has been frequently mentioned as one of the main compounds of EOs with antimicrobial activity, showing, in some cases, a broad spectrum of activity and synergistic effects with other terpenes. Although the data must be complemented by antimicrobial activity studies on the pure molecule or by a High-Performance Thin Layer Chromatography (HPTLC) bioautographic assay [112, 113, 114], the preliminary activities collected in this study represent, in our opinion, an interesting starting point encouraging further research. Antitumoral activities have also been frequently mentioned as a promising field of study, both for pure molecules and EOs rich in alpha-phellandrene. As reported by [PERSON] et al. [115], several searches have focused the in vivo anticancer activity of terpenoids contained in EOs, including some promising clinical studies on humans. The mode of action seems to be related to the activation of proapoptotic processes in the mitochondria in cancer cells, inhibition of tumor-inducing genes and production of free radicals in cancer cells. Additionally, EOs present minor undesired effects on healthy cells, probably due to a regulation of liver detoxification enzymes. Another study, performed by [PERSON] et al. [116], investigated the preventive and therapeutic activity of various EOs and their components against colorectal cancer (CRC), showing interesting preliminary results with carvacrol, geraniol, cinnamaldehyde and beta-caryophyllene. Taken together, these results suggest new therapeutic approaches, which involve EOs or their individual compounds, in CRC prevention and treatment, and the possibility to explore decreasing the doses of common chemotherapy drugs with the related side effects.