Dioxin is the name generally given to a class of super-toxic chemicals.
You will not see this chemical name on an ingredient listing. It is often contained in antibacterial ingredients such as triclosan, emulsifiers, PEGs and ethoxylated cleansers such as Sodium Laureth Sulfate. By binding to a cell's hormone receptor, dioxin literally modifies the functioning and genetic mechanism of the cell, causing a wide range of effects, from cancer to reduced immunity to nervous system disorders to miscarriages and birth deformity. The tiniest amount can cause damage, and our bodies have no defense against it. The most visible example was Yushchenko, the new Ukrainian President, who suffered from dioxin poisoning and seemed to age overnight.