Although polyunsaturated fats are generally thought of as healthy, there are at least two possible exceptions to this statement. One is that there is some evidence that polyunsaturated fat, in excess, can contribute to cancer risk. It is thought that the reason for this may be that polyunsaturated fats turn rancid more quickly than other fats. Therefore, proper storage of oils with high amounts of polyunsaturated fats is recommended. Store in a cool, dark place before opening, and in the refrigerator after opening.
The other potential issue with polyunsaturated fats is that of the two main types of polyunsaturated fat, the amount of omega-6 fat that we tend to consume has increased dramatically in recent decades, while in general the amount of omega-3 fat we consume is lower. Some experts feel that this imbalance is contributing to inflammation in our bodies, and increasing the risk of such chronic diseases as arthritis, diabetes, and heart disease.