What is Idiopathic Gynecomastia About half or more of the cases of gynecomastia for which no clear cause can be found and all hormone measurements are normal are called idiopathic gynecomastia, but it is important to note that some of these patients may have had transient feminizing factors that were no longer present at the time of the visit. They may have been exposed to small amounts of estrogenic or anti-androgenic substances in their work and living environment or may have had a history of mild endocrine dysfunction. The disorder may be related to environmental contaminants, some of which are estrogen-like compounds, such as organochlorine pesticides and dioxin-like compounds, which can enter the body and produce sex hormone-like effects.