Doctors in Austria have announced that Ukrainian presidential candidate Viktor Yushchenko (search) has been poisoned with dioxins. This is what dioxins are and how they affect human beings:

— Dioxins are a group of chemicals produced as byproducts from factories that use chlorine or from incinerators. They are widespread in the environment and low doses accumulate in the body, mostly through food.

— The most hazardous dioxin is tetrachlorodibenzoparadioxin (search), or TCDD, an ingredient of Agent Orange (search), which was linked to health problems in Vietnam veterans and local villagers exposed to it. Chronic exposure is believed to multiply the risk of several cancers, increase the chance of immune system disorders and liver problems.

— Most of what's known about the health effects of acute doses comes from studies on animals.

— Chloracne — an adult form of the skin condition — is the most widely recognized and consistently noted effect of high dose exposure in humans. It can disappear after the poison wears off or it can persist for many years. It is not a health hazard.

— Other effects from high dioxin doses in humans include decreased liver function, an enlarged liver and slight increase in blood fats, though both effects tend to be mild and short-lived. Doctors said dioxin levels in Yushchenko's liver have now returned to normal and he is expected to be released from the hospital in the next few days.

— Dioxin poisoning can also increase the risk of diabetes.