Is it harmful to inhale baby powder?
Inhale enough of it often enough Yes.
Any amount inhaled is harmful:
Tricalcium Phosphate when inhaled is harmful. Here is the proof. This is a Material Safety Data Sheet (MSDS) which states:
"The substance is toxic to lungs, mucous membrane."
Frequent exposure may cause particulates to lodge in the lungs. One case showed crystallosis in the lymph glands of a woman who used dental powder containing Tricalcium Phosphate. Beta TCP has been banned, in some forms, for use as a bone filler.
Use only pure cornstarch as baby powder, if you use anything. Rotate the bottle with your wrist intsead of shaking the bottle. The powder will tumble through the holes gently. Never shake the powder. ANY particulate can be unhealthy when inhaled.
The only options you have after inhaling baby powder is to blow your nose several time (not too hard) because the hairs inside the nose are there to catch particles. You can also sip warm water and spit it out if you feel you got some of the baby powder in your mouth. Baby Powder has been questioned as not being safe for babies and another good alternative is simple baking soda.