In addition to the three main types of oestrogen produced by the female body oestrone, oestriol and oestradiol (the most potent and plentiful), scientists have discovered that the body produces two different chemical types of oestradiol: 2-hydroxyoestrone, a "good oestrogen" that reduces the risk of breast cancer, and 16 alpha hydroxyoestrone, a "bad oestrogen" that can trigger or stimulate the development of cancer.

The same factors that influence the total amount of oestrogen in the body diet, medication, reproductive patterns and lifestyle also influence the balance between good and bad oestrogens in the bloodstream.

High levels of oestrogen flow through your body from the time of your first period until you pass through menopause, for an average of about 40 years. This time period is what we call your "natural oestrogen window".

Three oestrogen related factors contribute to your risk for developing breast cancer.

Overall oestrogen level: The total amount of oestrogen to which you are exposed over the course of your life, including natural, synthetic, pseudo and phyto oestrogens.

Duration of exposure: The length of time you are exposed to oestrogen, which depends on how many children you bear, whether you breastfeed and other reproductive factors.

Balance between the "good" and "bad" oestrogens.