Talc is considered extremely toxic and is closely related to the potent carcinogen asbestos. The main issue for babies is the possibility that they will inhale this (not to mention you) and those particles will get in the lungs. If inhaled, it can lead to allergic reactions similar to hay fever.
"For the last 30 years, scientists have closely scrutinized talc particles and found dangerous similarities to asbestos. Responding to this evidence in 1973, the FDA drafted a resolution that would limit the amount of asbestos-like fibers in cosmetic grade talc. However, no ruling has ever been made and today, cosmetic grade talc remains non-regulated by the federal government." – Cancer Prevention Coalition
For all the above reasons we don't use Talc in our baby powder - instead we use certified organic tapioca starch which effectively keeps baby dry and comfortable without all the hazards associated with Talc - read more and purchase here.