Peace be upon you. It is permissible to wipe over the skin of the head or the front of the hair. However, if the hair from other areas of the head is gathered at the front or if the front hair is long enough to spread over the face or shoulders, then it is not sufficient to just wipe over it. In such cases, one must part the hair and wipe over the skin of the head or the ends of the hair. Sources: Ayatollah Khamenei: Answers to Religious Inquiries, S125. Ayatollah Sistani: Official website.