(Negative すぎる 'too much') when to use なすぎる and なさすぎる


I understand there are two forms meaning 'too little' or too few', I thought
the regular way to conjugate the negative was ない-form verb, and the last い is
replaced with さ, making なさすぎる. (e.g 食べなさすぎる) But at the end of the chapter it
says you can also use なすぎる with 'most regular i-adjectives'such as 危なすぎる 'not
too dangerous'. Please can someone explain this to me.

