(via Canon U.S.A. : Support & Drivers : Consumer & Home Office)
The front rubber grips of some EOS REBEL T4i units produced in certain lots between May 31st through June 27th, 2012 may turn white after a short period of time. We have determined after inquiry with the rubber manufacturer and analysis, that the white substance is zinc bis (N,N’-dimethyldithiocarbamate).
Caution on Use
The amount of zinc bis detected during our testing was minimal. It is possible for zinc bis, in the small amount found in the camera grips, to cause allergic reactions, such as a rash, when it comes in contact with skin of sensitive persons. In addition, if eyes are rubbed after contact with the substance, symptoms such as red eyes may develop. As a precautionary measure, thoroughly wash your hands with water if they have come in contact with a rubber grip that has turned white. If any medical symptoms develop, please consult your physician immediately.