Guayulins from Parthenium argentatum, A. Gray (guayule): Novel potential active ingredients for cosmetics

Guayulins, a family of sesquiterpenes derived from the resin of Parthenium argentatum, A. Gray (guayule), hold promise for stimulating the industrial cultivation of this shrub in European semiarid regions. Their antibacterial and antioxidant properties make them appealing to the cosmetics industry, which increasingly seeks natural alternatives. However, conflicting studies on skin sensitization has raised concerns about their potential to cause allergic reactions. To investigate the cosmetic potential and safe dosage of guayulins, a series of tests were conducted on a human keratinocyte cell line (HaCaT). Our findings reveal that for safe cosmetic applications, guayulins should be used below 20 μM, with the consideration that the dose-response is time-dependent, with guayulin C being the most cytotoxic. Cellular antioxidant assays and skin regeneration tests demonstrated significant activity of guayulin D at doses of 3.15 µM and 20 µM, respectively. Direct Peptide Reactivity assays showed varying sensitization potential between guayulins: B (low), D (moderate), and C (high), with guayulin A results limited by solubility issues. These findings highlight the promising cosmetic potential of guayulins and underscore the need for further studies to ensure their safety and efficacy in human applications. • Guayulins as potential active ingredients for cosmetics. • Significant activity for guayulin D in cellular antioxidant assays and epidermal regeneration tests. • Guayulins concentration below 20 µM does not show cytotoxicity in keratinocytes. • The DPRA revealed that guayulins B, C, and D could be allergenic, guayulin A needs further determinations.