Steroid hormones like estrogen (or its mimics) work by entering the cell and binding to a receptor.
The hormone-receptor complex binds to DNA in the cell nucleus.
This binding activates a gene, which directs the production of a protein.
A new protein is made, and the protein causes changes in the cell's activity.
An endocrine disruptor works by binding with the hormone and preventing it from ever binding with the receptor.
Since the receptor is never bound, no genes are activated and no proteins are formed. The cell does not change. This has serious implications for fetal and child development.