All mammals naturally produce hormones, these play vital roles in reproduction, development, and metabolism. There is growing concern that with more and more chemicals being added to the environment, some of these chemcials are altering our hormones. The main concern is that throughout the animal world there is increasing "feminisation". These feminisation effects caused by synthetic hormones were demonstrated by a 5 year study of 10 rivers by the UK Environment Agency. This showed that 50% of male fish had developed eggs in their testes, 10% were sterile, 25% producing damaged sperm.

There are two issues to consider, synthetic hormones found in plastic packaging and the application of hormones in agriculture.

Synthetic hormones interfere with our natural hormones and have the ability to cause effects such as sterility, abnormal sex differentiation and cancer. Synthetic hormones are products of the petrochemical industry. In addition to agricultural use they are found in many everyday products. They can leach out of plastics used to package food.

Naturally occuring hormones include Vitamin D, hormones are found in milk - cows could not produce milk without them. Livestock are treated with both naturally occuring hormones and substances that imitate the action of natural hormones. This increases milk yield and accelerates the growth of animals so that they 'bulk up' faster and reach market earlier. The most effective growth promoters are natural sex hormones such as Testosterone and Progesterone, these are regularly applied to animals in some countries.

The EUs Scientific Committee on Veterinary measures relating to Public Health (SCVPH) consider there is a substantial body of evidence suggesting that oestradiol 17ß has to be considered as a complete carcinogen (exerts both tumour initiating and tumour promoting effects).