Cetaphil may kill SOME lice but it doesn't kill any nits. Furthermore it requires many treatments. Nothing on the market kills all lice and eggs. Finding a quality product that aides in the removal as well as a quality comb is most important. See products page for Nit Free Treatment Kit and Comb.
While children more commonly get head lice, adults are not immune. All family members in the same household should be checked for lice. I have treated many Moms as well as Grandparents.
Head lice actually prefer a clean head of hair and healthy scalp. Lice, however, do not discriminate. A louse’s only concern is for its own survival. To accomplish this, the louse needs to feed and is always looking for the most convenient means of doing so.
Hair products do not prevent someone from getting lice. Though lice may prefer a clean head, using products does not deter them. Invest instead in a quality mint repel spray, which is an offensive odor to lice. Refer to products page for Nit Free Mint Repel Spray.
Don't treat needlessly. Instead get everyone checked by a professional so your time and resources can be spent treating the ones that actually have lice. I only recommend treating those that actually have nits or bugs found in their hair.