A bit of insight on what I see in this photo - there's a calcimine coating as well as lead paint (you can test it for lead for kicks, calcimine is less harmful - used to be used as a washable coating for ceilings etc when we burned coal or wood inside) - the calcimine is the unstable coating (if you have any other old ceilings in your house that aren't covered they may develop a pattern like this but on a way lesser scale as they're coated more recently). The instability of those ceiling coatings means that it will all come off.. In very small and particulate pieces.