The active component of Castor Oil is ricinoleic acid. Castor Oil is composed approximately of 75-85% of this fatty acid. It has a molecular weight of 298 daltons. In dermatological medicine there is what is called the 500 Dalton Rule. Substances that are below 500 daltons can permeate through the lower layer of the epidermis, which is the top layer of the skin. It can then go deeper, into the dermis, that contains the blood and lymphatic vessels. These are the superhighways of the body, transporting medicinal substances like Castor Oil into the body. Compression also helps to put tension on the skin, facilitating its deep penetration. So using the pack is a very important part of the treatment.