It describes an extraction process for obtaining a standardized extract of quercetin and 3-0-methylquercetin from inflorescences of macela- do-campo (Achyrocline satureioides) characterized by comprising of the following steps: A) grinding the inflorescences of Achyrocline satureioides to obtain a material of ground plant; B) submitting the ground plant to at least four sequential stages of hydro-alcoholic extraction at a temperature from 60°C to 80°C1 for 3 to 4 hours for each stage, in order to obtain 4 intermediary hydro-alcoholic extracts; C) combining the 4 intermediary hydro-alcoholic extracts; D) concentrating the intermediary hydro-alcoholic extracts mixture; in order to obtain up to a maximum of 20% of the initial mass of the intermediary hydro-alcoholic extracts; E) drying the material obtained in (D). It also describes cosmetic, pharmaceutical and veterinary compositions containing the aforesaid extract of macela-do-campo, destined for the prevention and treatment of the damages arising from inflammatory, microbial and oxidation/lypoperoxidation reactions. The use and method of application of the aforesaid extract of macela are also described.