You're thinking of Hydroflouric Acid, not flouride. https://www.atsdr.cdc.gov/toxguides/toxguide-11.pdf Almost 100% of inhaled hydrogen fluoride is absorbed through the upper respiratory tract; it is likely that fluorine will also be well absorbed. - Soluble fluoride compounds are well absorbed (80–100%) through the gastrointestinal tract. Insoluble fluoride compounds are poorly absorbed (<10%). - Hydrofluoric acid is absorbed through the skin. - Once absorbed, fluoride is distributed throughout the body, with the highest concentrations found in calcified tissues. - Fluoride is not metabolized and is eliminated via the urine.