Does using ointment and bands containing medicine invalidate the fast?
Oil, ointment and similar things applied on the skin are absorbed through the pores and capillaries under the skin and mix with blood. However, the skin absorbs them in very small amounts and very slowly. On the other hand, it does not mean eating or drinking. Therefore, the ointment applied on the skin and the band containing medicine that is stuck on the skin do not invalidate fasting.
