## 1 Introduction  
The antimicrobial and antioxidant properties of essential oils (EOs) and their hydolates (Hys) have been recognized for more than 60 years, and have been applied in different fields such as cosmetic, food flavors, cooking, therapeutic, perfumery, and active packaging [1, 2, 3, 4]. Extensive reviews were published on EOs and Hys biological properties and potential applications [5, 6, 7]. In recent years, several scientific papers faced the problem of biodeteriogenic microorganisms, both at the laboratory scale [8, 9] and in real cultural heritage areas [10]. In these concerns, EOs were applied in the vapor phase for two hours in an unventilated indoor space, and the microbial contamination was monitored after a maximum of 24 h. Moreover, as reviewed by [8], treating paper items with oil in the vapor phase allows us to avoid significant damage in terms of color alterations or pH acidification. The antimicrobial effect of EOs in the vapor phase can be expressed by means of the minimum inhibitory dose (MID), that is, the minimum dose in the gaseous phase able to inhibit microbial growth [11]. MID, a parallel method to the minimum inhibitory concentration (MIC) for EO in liquid phase, must be evaluated in a sealed container at a controlled temperature since it depends on the amount of the volatile components in the vapor phase. A slow evaporation rate can be obtained by placing the pure EO in a (glass) container, while a more rapid evaporation rate can be obtained by using different methods: through a filter paper impregnated with pure or diluted EO (e.g., in ethyl acetate or Dimethyl Sulphoxide (DMSO)) or by spraying small droplets that immediately turn into vapor [12]. Since heating the EOs can destroy or modify some of their components and thus can affect their antimicrobial efficacy, temperature control is a fundamental issue [13]. [PERSON] et al. [14] investigated the antimicrobial activity of _Ocimum basilicum_, _Origanum vulgare_, and _Thymus vulgaris_ EOs against 13 bacterial strains using the agar diffusion method, and against 6 fungal strains using the microdilution method. All of the tested EOs exhibited a low minimum fungicidal concentration (MFC) for some fungal strains, which was lower than the value obtained for bifonazole, a broad-spectrum antifungal drug; thyme and oregano EOs showed higher antimicrobial activity, probably due to the similar chemical profiles in which phenolic monoterenes are the major components. In particular, carvacrol and thymol showed an antimicrobial effect against both Gram-positive and Gram-negative bacteria and fungi, and they also exhibit antibiofilm activity. [PERSON] et al. [15] investigated the antimicrobial activity of six EOs, containing different concentrations of phenolic components, against pathogenic and environmental bacterial strains and five different fungi, representative of microbial contaminants in the indoor air. Among the tested EOs, oregano, thyme, clove, and arborvitea showed very strong antibacterial activity against all tested strains. The EOs exhibited fungistatic and fungicidal activity depending on the applied method; in particular, their application in the vapor phase showed fungicidal activity. This result agrees with the growing evidence that EOs in the vapor phase are more effective against fungi [16; 17]. The results confirmed those reported by [PERSON] et al. [18], which was related to the in vitro activity of some EOs against clinical and environmental fungal strains. The MIC was determined by a microdilution method and by a vapor contact assay. Results indicated that the EO activity depended on the experimental assay used and the EO inhibition in the vapor phase being higher than that of the liquid one. Also, in this case, thyme red and clove showed the widest spectrum of activity against all tested fungi. [PERSON] et al. [19] studied the antifungal activity of the thyme EO and pure thymol on different genera of molds isolated from damp dwellings: _Aspergillus_, _Penicillium_, _Alternaria_, and _Trichoderma_.