Sounds very much like termites or wood worm. Find a good exterminator or if you can’t afford see what you can get from a hardware store.
NO NOT TERAMITES inside your door is cardboard and somehow moisture got into it and the rotten dried remains is what is falling out replace the door or just take some wood puddy and cover the bottom of the door there might e a hole there may the bottom was shaved down for carpet and that is how moisture is getting in side
Probably termites, get them out quick, Maybe the best solution is to replace the door, and the frame. Also call an exterminator to check it first.
Sounds much like termites. Also wouldn’t be unlikely that its wood rot if its an exterior door or any other door that gets moisture. It could be that the bottom of the door wasn’t sealed and you can get a wood sealer and that will help your problem if its wood rot. Have a exterminator check it out, there are some out there that will examine for free or very little charge.
most interior doors ARE hollow. must be rubbing against something to wear it out.
What looks like wood “grains” is termite *****. Unless its an expensive, solid core door, your best solution is to replace it. I would have an exterminator check the rest of your house for termites. It is inlikely they are only in the door.
the first thing i would do is take the door off and see just what is going on under there…