App note from ONSEMI about proper handling of IGBTs, the main issue is that static can build-up on IGBTs gate-source junction enough to damage it, discussed also in this app note on ways to safely work with IGBTs. Link here (PDF)
One of the major problems plaguing electronics components today is damage by electrostatic discharge (ESD). ESD can cause degradation or complete component failure. As circuitry becomes more complex and dense, device geometries shrink, making ESD a major concern of the electronics industry.