Castor oil is an effective laxative that comes from the seeds of the castor plant (Ricinus communis) and is made by pressing the ripe seeds from the plant once their outer hull has been removed (the hull contains ricin, a poison). Castor oil once was given routinely to children to help "boost their health." Its main constituent is ricinoleic acid, a fatty acid that binds with two specific receptors that can set off intestinal contractions that promote bowel movements as well as uterine contractions to induce labor.
Over the years, castor oil has been used for a wide variety of medicinal purposes. In addition to its roles in relieving constipation and inducing labor it has been used to promote the flow of breast milk after the birth of a baby, for birth control, and as a treatment for leprosy and syphilis. It has also been used topically to treat boils, acne, and inflamed skin, to soften bunions and corns, and to remove warts. I have read that it can soften cuticles, soothe tired eyes, and condition hair. However, I’ve seen no scientific evidence that it works for any of these other purposes.
I discussed your question with Tieraona Low Dog, M.D., an internationally recognized expert in the fields of integrative medicine, dietary supplements and women's health, and an authority on botanical medicine. She notes that she has seen no studies showing that applying castor oil to the skin is an effective treatment for acne and cautions that it should be used only infrequently to relieve constipation, adding that there are better treatments for both.
I’ve never heard of using castor oil to relieve upset stomach except possibly in the form of warm castor oil packs placed on the belly. The heat may do as much good as the oil itself.
For acne, I recommend washing regularly and gently with mild glycerin soap. If you want a natural substitute for cleansing agents containing the anti-acne preparation benzoyl peroxide, I suggest using calendula, commonly known as pot marigold. You can find calendula skin products at health food stores. You may also try washing with a five percent solution of tea tree oil, also available at health food stores.
Andrew Weil, M.D.