“…Although there are different methods for quantifying MB and MET in their isolated form or associated with other substances (Chengalva, Angala Parameswari, & Aruna, 2016;Chengnan et al, 2019;Chhetri, Thapa, & Van Schepdael, 2014;Khdair, Handa, Mao, & Panyam, 2009;Prasanna & Priyanka, 2015;Rengelshausen et al, 2004;Rostamkalaei, Akbari, Saeedi, Morteza-Semnani, & Nokhodchi, 2019;Umapathi, Ayyappan, & Darlin Quine, 2012;Wang et al, 2009), few studies quantify these substances in a matrix as complex as the skin (Chen et al, 2020;Garcia et al, 2018;Junqueira et al, 2016;Polonini et al, 2019;Yu et al, 2018Yu et al, , 2019 and some of them employ quantitative methods that are not selective (Garcia et al, 2018;Junqueira et al, 2016) or standardized for other matrices such as plasma and urine, which may not be suitable for quantification in the different layers of the skin (Yu et al, 2018(Yu et al, , 2019; moreover, there are no studies in the literature that quantify the two substances simultaneously and in the different layers of the skin (SC and viable epidermis + dermis, VE + D).…”