There are several things to look for when selecting an oil based product and specifically Evening Primrose Oil. First, you want to make sure that the label clearly states details about how the oil was extracted. Many companies will use harsh chemicals to extract the oil because it can greatly speed up the process. Choosing a hexane free product guarantees that no harsh chemicals were used in the extraction process.
The label should also state that the product was cold pressed. When any oil is exposed to excessive heat it can greatly degrade the quality of the oil, making it rancid. Rancid oils can be harmful to your health by creating oxidative chain reactions. Cold pressed implies that the company used a process that minimizes the use of heat in the extraction process to preserve the quality of the oil.
The important thing is to make sure you are purchasing the product from a company you trust. If you have questions about the extraction process or the product call the company to find out more details. Good companies should be able to provide you with all the information you need to be comfortable with the product.