A common chemical ingredient in plastics has been linked to smaller penises and incomplete descent of testicles in baby boys.
Phthalates, which are added to plastics to keep them soft and pliable, are linked to a feminizing effect on boy fetuses whose moms had above-average levels of the chemical in their urine while pregnant.
Moms who had the highest amounts gave birth to boys with more feminine characteristics.
Scientists have been concerned about the effects of the phthalates, known as DEHP, because rodent studies showed it had a negative effect on the masculinity of young rats.
Current research conducted in three different areas of the United States, showed their concerns were well-founded. Scientists found a definite correlation between levels of the chemical in pregnant moms and a feminizing effect on their sons. They theorize that phthalates may reduce testosterone synthesis.
Phthalates are added to many personal care products including perfume, nail polish and hair spray. They are also included in many cosmetics,but the consumer is unaware because they are not specifically listed on the label, hiding under other items such as fragrances.
Source, tl;dr version, tl;dr version II