Australia denounced on Tuesday accusations that experimental vaccines used on Australian servicemen during the Gulf war could have resulted in Gulf War Syndrome. An unknown number of Australian solders say they have Gulf War Syndrome, which can cause pain, fatigue, irritability, and sleep difficulties. Some experts believe the syndrome was caused by exposure to depleted uranium, Iraqi chemical weapons, and smoke from burning oil wells, but one study suggests that squalene, a substance used in some vaccines to boost the immune response, could be the cause. A spokesman for Veterans Affairs Minister Bruce Scott noted that the Australian Defence Force (ADF) has never used squalene, and he added that the immunization schedule for ADF "task group deployments [in] 1990-91 did not include any experimental or unregistered vaccines."