Firstly, it is important to clarify that a scar cannot completely disappear with the application of castor oil or any other compound. Only laser treatment is effective in completely removing a scar (and even then, this depends on its severity).
Next, regarding the effects of castor oil on scars, very few scientific studies currently exist on this subject using human skin explants. A study on the healing properties of pure castor oil involves the reduction of a significant wound in an elderly horse. It has been demonstrated that castor oil has bactericidal, healing, repelling, and larvicidal properties. Regarding the application of castor oil on human skin, a retrospective study involving 36 patients who underwent a skin graft examined the effects of a combined ointment containing castor oil, Peru balsam, and trypsin. According to the researchers, this ointment may improve healing. However, it is difficult to determine which compound actually influenced the healing, or if the result is due to a synergy between the three ingredients.
Thus,castor oil could potentially be relevant for topical application during the healing of a minor wound. Indeed, ricinoleic acid, a mono-unsaturated fatty acid present at about 85%, will combat bacterial colonisation and therefore prevent a minor lesion from becoming a significant scar.
How to use it? Daily, morning and evening, apply it to the targeted area and perform massages to enhance its absorption.