Earlier this month, Canon issued a product advisory on the Rebel T4i for an error in the firmware.  Two days after the issuance of that advisory, Canon issued another product advisory for the Rebel T4i with regard to the presence of zinc bis in the rubber grip.

In short, this substance may cause the rubber grips to turn white and could potentially lead to skin allergies or irritation.  The lot affected can be identified by looking at the serial number.  If the sixth digit is "1" then your camera could be affected.

Specific details in the full product advisory below.

[via Canon USA]

Thank you for using Canon products.

The front rubber grips of some units of the Canon EOS REBEL T4i Digital SLR camera (EOS 650D/EOS Kiss X6i overseas models) may change color (turn white) after a short period of time. Customer support for this phenomenon is described below.

Canon continuously strives to provide our customers with high quality, reliable products that can be used with confidence. We offer our sincerest apologies to any customers who may be inconvenienced.

Phenomenon
The front rubber grips of some EOS REBEL T4i units produced in certain lots during the sixteen-day period between May 31st through June 15th, 2012 may turn white after a short period of time. We have determined after inquiry with the rubber manufacturer and analysis, that the substance zinc bis (N,N’-dimethyldithiocarbamate) is what causes the rubber surface to turn white.

Zinc bis is not used in the production of this product. However, the quantity of rubber accelerator used in the affected production lots was slightly higher than usual. As a result the rubber grips may turn white due to a chemical reaction with the rubber accelerator and other substances. High temperature and high humidity may contribute to this condition. Zinc bis (N,N’-dimethyldithiocarbamate),…