estrogens do occur in these type of matrix, natural estrogens obviously being more present than synthetic or estrogen-like compounds. A good percentage of works have analyzed real samples, even studying how the netural-estrogen level changes with respect to gestation period or fat content. Despite this, and due to the importance of such evidence, more works concerning the determination of estrogens, especially their metabolite, in these samples are still needed. Future approaches should especially focus on this vital aspect to ensure safe consunption of milk and milk derivatives.