In September 2004, Viktor Yushchenko, Ukraine’s leading opposition presidential candidate, became seriously ill during a bitter election campaign.

He developed severe abdominal pain and other symptoms, and his face later became covered with painful, disfiguring skin lesions.

On December 11, Austrian doctors confirmed that his illness was caused by dioxin poisoning, with tests revealing extraordinarily high concentrations of the toxic chemical in his body.

The substance was identified as TCDD, one of the most toxic dioxins known.

It can persist in the human body for years and, at high exposure levels, cause chloracne, a severe skin condition that produces cysts, inflammation and lasting scarring.

Yushchenko’s facial transformation became one of the most recognizable features of the political crisis.

The suspected poisoning occurred during a campaign that divided Ukraine between supporters of closer ties with Europe and those favoring stronger relations with Russia.

After the disputed November 2004 presidential runoff, mass protests erupted over allegations of electoral fraud.

The movement became known as the Orange Revolution, and Ukraine’s Supreme Court eventually ordered a new runoff election.

Yushchenko won the December vote and became president in January 2005.