Does a menstruating woman have to change her clothes after her period ends, if no blood or najaasah (impurity) has gotten on them?.
She does not have to do that, because menses does not make the body naajis (impure); rather menstrual blood only makes naajis what it touches. Hence the Prophet (peace and blessings of Allaah be upon him) enjoined women, if any menstrual blood gets on their clothes, to wash them and pray in their garments. End quote.
Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him)