Evening Primrose oil is derived from the oenotheraas biennis, a small yellow wildflower that is now cultivated to produce the oil.
You do not need a lot of this oil in your soap recipe for it to be beneficial. Adding 5 - 10% of your total oils at the start of the soap making process should be sufficient.
The chart below shows the approximate percentages of fatty acids present in Evening Primrose Oil. This is a great oil to add to soap for its conditioning qualities of which it has plenty.
This information is provided for reference use only and is not meant to substitute the advice of a licensed health care professional.