Kevin from what I can see the active ingredient in most flea shampoos is either permethrin or pyrethrin, or pyrethrum. All of these are from the extract of the Chrysanthemum flower.
per Wikipedia
Exposure to
pyrethrum, the crude form of
pyrethrin, causes
harmful health effects for mammals. ... Exposure to
pyrethrum in high levels in
humans may cause symptoms such as asthmatic breathing, sneezing, nasal stuffiness, headache, nausea, loss of coordination, tremors, convulsions, facial flushing, and swelling.
For me personally I keep Diatomaceous Earth. I grow Catnip, Chamomile, Citronella and Chrysanthemums, Mint and Marigolds around my property and rarely have flea problems. Also make great tea. I throw these flowers and herbs in my chicken house to deter chicken mites also.
https://www.vulcantermite.com/home-pest-control/plants-that-repel-fleas-where-to-put-them/
For head lice/body lice here are some ideas using things that should be in your preps anyway. Olive oil,coconut oil, apple cider vinegar, aloe gel etc. You could store a few essential oils and rub on your body or put in a bath. Even add herbs to your laundry that would discourage body lice.
https://theherbalacademy.com/lice-home-remedies-using-herbs/
Essential oils that have shown a high percentage of effectiveness are anise seed, cinnamon leaf, tea tree, oregano, red thyme, sweet orange, clove, eucalyptus, geranium, lemongrass, peppermint, and nutmeg. Essential oils are extremely potent combinations of chemical constituents and great care should be taken when using them. Not all essential oils are safe for all ages, so if treating for lice on children, it is important to make sure you are taking extra precautions for safe use (for more on essential oil safety for kids, please see our
recent post here). Do not use essential oils on anyone without diluting them in oil first and always buy from a
quality source.
I would shy away personally from using flea shampoos on my body regularly for fear that the active ingredients would be absorbed through the skin when used regularly causing skin irritation and possible health problems.