The head louse problem increases at all levels of the international societies due to activities or life conditions that lead to often hair contacts among people. Lice occur exclusively on humans. Thus, they avoid dropping down from a head and therefore accept even a bad smelling hair of new a host. Due to this behaviour, there are only a few products on the markets which dare to claim a repellency activity that protects humans from infestation with head lice. The present study shows that a combination of an extract of the seeds of the plant Vitex agnus castus (monk pepper) and the compound paramenthan-3,8-diol (which is also found in some plants, e.g. Eucalyptus) act synergistically and are able to protect human hair for at least 7 h from invasion of head lice (Pediculus humanus capitis). The recently developed product containing both compounds is named Licatack Preventive Spray.