What it is: Bio-Oil is an award-winning specialist skincare product that is clinically proven to improve the appearance of scars, pregnancy stretch marks, and uneven skin tone. What it does: Bio-Oil includes the breakthrough ingredient PurCellin Oil, a recreation of the preen gland oil of ducks. During preening, a duck secretes oil from its preen gland and distributes it over its entire plumage in the familiar twisted-neck action that one often associates with ducks. What else you need to know: For external use only. Do not use on broken skin.