Before a woman immerses in the Mikveh, she must thoroughly wash her hair and her body to ensure that there is no chatzitzah (substance that obstructs the water from coming in contact with the body). Ha’Rav Ovadyah Yosef (a”h) was asked about a case involving a woman who after immersing in the Mikveh, noticed some suds behind her ear or behind her neck, which she had apparently neglected to rinse off after she bathed. Are the suds considered a chatzitzah and requiring of her that she immerse again after removing them?
Rav Ovadyah addressed this question in his sefer, Taharat Ha’bayit, where he writes that the immersion in such a case is valid. He explains that since water is able to penetrate the suds and come in direct contact with the woman’s body, the suds are not considered an obstruction. He compares this case to the situation of a woman who immerses with oil on her skin or with honey that had not yet dried, in which case the immersion is considered valid. A liquid substance on the skin does not constitute a chatzitzah because it does not block the water from coming in contact with the skin. This applies to suds as well.