It depends on what kind of powder. If talcum powder is used, then it is hazardous as talcum powder can cause ovarian and lung cancer. This is actually a possible science project for me so i have researched this.
Many people had talcum powder put on them as babies, but now there is controversy surrounding it and many do not believe that it is safe. The powder has been linked to cancer and is not healthy for a baby to ingest.
It would be quite unfortunate if it were, because then we would have inadvertently maltreated an entire few generations of babies ... (talcum powder is just baby powder). If you're asking if talcum powder is dangerous when ingested, that is a different story.
It can be - baby powder (talcum powder) is a fine particulate material, which means it can get deep into a cat's lungs and cause problems. Also, it is a calcium salt, which if ingested can cause electrolyte issues.