The invention primarily concerns an extract of a plant belonging to the Asteraceae family, for example of the Dittrichia genus, which is essentially characterised in that it comprises at least the compound 12-carboxyeudesma-3,11(13)-diene and/or one of the dehydrogenated derivatives of same acting as an antifungal agent, and in that it is obtained according to a method comprising at least the steps of drying the fresh plants, macerating the dried plants in a solvent chosen from water, alcohols, ketones, esters, ethers, chlorinated solvents, hydrocarbon alkanes and any mixture of two or more of the cited solvents, or by supercritical fluid extraction optionally combined with a co-solvent, and drying the mixture, the operating temperature of said steps being less than 60 °C and the pH of the maceration step being 1 < pH < 10.
