The possibility that topical fluorides can provoke inflammtory skin disorders gains is supported by carefully controlled studies on animals.
When topical fluoride has been applied to the skin of rabbits or rats, inflammation has been repeatedly noted when the skin is cut or damaged prior to the application.
Studies Examining Fluoride-Induced Inflammation of Skin in Animals
“Application of ammonium fluoride under an occlusive patch to the abdomen of a rabbit converts a simple scratch into a double row of sterile pustules. Sodium fluoride produces a similar response, but ammonium chloride does not produce pustules… It appears that tissue damage and the presence of fluorides result in the ‘sterile pustular response.’ This can be called ‘enhancement of inflammation.’ The concentration of fluoride used will not induce inflammation, but it will enhance inflammation… We are not stating that iodide, fluoride, and nickel necessarily enhance inflammation in identical ways, but there is no doubt that they all enhance the inflammatory response. The fact that each of these substances produces the pustular patch test in man indicates that the reaction is not limited to animals.”
SOURCE: Stone OJ, Willis CJ. (1967). Enhancement of inflammation by fluorides. Texas Reports on Biology and Medicine 25: 601-6.
“Scratches were made to the depth of the upper dermis on the abdomen of rabbits. The scratches were covered by patch tests for 18 hours with solutions of stannous fluoride or stannous chloride. Both these substances produced a destructive reaction with intraepidermal polymorphonuclear leukocyte pustules occurring on each side of the scratch. Stannous fluoride was destructive at lower concentrations than stannous chloride. When these substances were patch tested over non-traumatized tissue, no tissue damage occurred… We believe that the metals and halogens that produce pustule along the scratch are damaging the body’s defenses against the mediators of inflammation and are therefore exaggerating the early cellular phase of inflammation… Dentrifices (toothpastes) are not made for prolonged contact with tissue; however, even brief exposure might influence preexisting oral pathology. Further clinical observations on the effects of fluoride dentrifices on oral inflammation are indicated.”
SOURCE: Stone OJ, Willis CJ. (1968). The effect of stannous fluoride and stannous chloride on inflammation. Toxicology of Applied Pharmacology 13: 332-8.
“Topical and systemic administration or contact with fluorides has produced various forms of cutaneous reactivity. These studies, conducted wtih 150-400 g. Sprague-Dawley rats, investigated the effect of topical application of NaF to a shaved, epidermal abraded region (5 cm) of dorsal skin. After 24 hrs. NaF (1%) produced inflammation of the epithelial keratin and the formation of intraepidermal vesicles abundant in fluid, polymorphonuclear leukocytes, lymphocytes, and erythrocytes. Edematous subendothelial changes were noted with cellular hypochromicity. Electron microscopy revealed extensive mitochondrial vacuolization. The cutaneous vesicles persisted for approximately 7 days after NaF application. In rats treated wtih NaF (23) skin histamine levels were significantly increased.”
SOURCE: Essman EJ, Essman WB, Valderrama E. (1981). Histaminergic mediation of the response of rat skin to topical fluorides. Archives of Dermatological Research 271: 325-40.
“OBJECTIVE: To describe the tissue response to implanted polishing and prophylaxis materials using a rat model system. MATERIAL AND METHODS: Two polishing pastes (diamond polishing paste and aluminum polishing paste), two prophylaxis materials (prophylaxis paste with fluoride and air polishing prophylaxis powder) and negative and positive controls were subcutaneously implanted in rats. Tissue specimens obtained after 2 days, 1, 4, 6 and 8 weeks after implantation were processed for routine hematoxylin and eosin staining and polarized light evaluation. RESULTS: Air polishing prophylaxis powder produced a mild inflammatory response. A more intense inflammation was elicited by diamond polishing paste, and the prophylaxis paste with fluoride elicited an even greater response. The aluminum polishing paste produced the most severe and persistent tissue response, which was of the granulomatous type. CONCLUSIONS: This finding suggests that foreign body reaction should be considered in a gingivitis that does not respond to plaque control or does not represent a mucocutaneous lesion.”
SOURCE: Tapia JL, et al. (2011). Inflammatory response to dental polishing and prophylaxis materials in rats. J Int Acad Periodontol. 13(3):86-92.