Is it obligatory for a woman to cover her head if she has completely shaved her hair or become bald due to illness, or is the head covering (hijab) based on the presence of hair?

A woman must cover and veil her head, even if she is bald or has shaven hair. This ruling is not affected by the presence or absence of hair, and there is no disagreement among scholars on this matter. It is not permissible for a woman to shave her head except in cases of extreme necessity.