Extensive research has shown that a number of UV filters frequently used in the formulation of commercial sunscreens, such as 4 MBC, octyl methoxycinnamate, oxybenzone (benzophenone-3), octyl-dimethyl-PABA and octinoxate, possess endocrine activity. Endocrine disruptors are chemicals that interfere with endogenous hormone action and/or production. These have been implicated in the development of a number of diseases in both males and females, including cancer of the mammary glands and reproductive organs, as well as the abnormal development of the male reproductive system. In one study, the application of three active ingredients commonly found in sunscreens (oxybenzone, 4-MBC and octinoxate) for one week led to a drop in testosterone and estradiol levels in men. More worrying is that these chemicals have been found in breast milk at concentrations known to have oestrogenic effects.