← The FormularySkin & faceHydroxyapatite
Also known as Microcrystalline hydroxyapatite · MCHA · calcium phosphateThe right mineral. The wrong address.
This is the clearest gap in the whole formula, so here it is. The trials that make hydroxyapatite interesting used a toothpaste that was 10% hydroxyapatite, brushed for 336 days in children and 18 months in adults. KISS has 5 mg, chewed once and swallowed: a small fraction of what one brushing puts against a tooth, with none of the repetition, and it will not do anything measurable to your enamel. As a swallowed calcium source it is 400 times below the 2 g used in a two-year bone trial. Two more things a reader should have. Both of those toothpaste trials were funded by Dr. Kurt Wolff GmbH, which makes the hydroxyapatite toothpaste tested, and the friendliest meta-analysis of the field was co-written by two of that company's researchers — its comparison against fluoride was not statistically significant. What I would tell a friend: if you want the hydroxyapatite evidence, buy a 10% hydroxyapatite toothpaste and use it as directed. The case for this chewable sits with the rest of it. It does not sit with these 5 mg.
The calcium-phosphate mineral that enamel and bone are largely built from. Ours is the microcrystalline form.
In toothpaste, hydroxyapatite particles deposit on the enamel surface, fill micro-defects and sit in saliva as a local calcium and phosphate reservoir. It works by contact, concentration and repetition: 10% of the paste, against the tooth, two or three times a day, for months. Swallowed hydroxyapatite does something else entirely. The EU's cosmetics safety committee notes that ingested particles dissolve rapidly in gastric fluid, and what crosses into you afterwards is calcium and phosphate ions, absorbed like any other mineral. That makes a swallowed dose a calcium source rather than an enamel one. A chewable does hold it against the teeth for as long as you chew, which is the only plausible local route, and nobody has tested that.
Contributes a trace of the mineral enamel is made of to a chewable built around xylitol, guava and a three-strain probiotic blend.
Honestly, nobody is taking KISS for the hydroxyapatite, and nobody should. It is for people who want the full chewable and would rather know what each part is doing. Not for anyone hoping it will repair enamel, and not for anyone treating it as a reason to skip a toothpaste.
Chew one thoroughly, ideally after a meal, and let it sit in the mouth rather than bolting it. It is not a replacement for brushing twice a day. The trial evidence for hydroxyapatite sits with a 10% toothpaste, and the comparator in those trials was a fluoride toothpaste; ask your dentist which of the two belongs in your bathroom.
Nothing you will notice, and nothing a dentist could measure.
Two non-inferiority RCTs carry the toothpaste evidence. In children (Sci Rep, 2021; NCT03553966), a fluoride-free toothpaste with 10% microcrystalline hydroxyapatite, used three times daily, was compared with a fluoride toothpaste over 336 days: 207 in the intention-to-treat analysis, 177 per protocol, an ICDAS increase of at least one code in 72.7% of the hydroxyapatite arm against 74.2% of the fluoride arm, exact one-sided upper 95% limit 9.8% against a 20% non-inferiority margin. In adults (Front Public Health, 2023; NCT04756557), a 10% hydroxyapatite toothpaste against 1,450 ppm sodium fluoride, brushed twice daily for three minutes over 18 months: 189 in the ITT analysis, 171 per protocol, no DMFS increase in 89.3% against 87.4%, upper limit 6.84%. Both trials were funded by Dr. Kurt Wolff GmbH, the manufacturer of the test toothpaste; the children's trial declared no competing interest, and three authors of the adult trial are company employees. A 2024 systematic review and meta-analysis (J Dent) favours hydroxyapatite over placebo at a pooled OR of 2.51, but its comparison with fluoride was non-significant at OR 1.1, and two of its six authors give the same company's research department as their affiliation. A 2025 systematic review (J Dent) found four eligible trials and no significant difference between hydroxyapatite and fluoride toothpastes on DMFS or ICDAS. The EU's SCCS judged hydroxyapatite (nano) safe in toothpaste up to 10% (SCCS/1648/22, March 2023) and up to 29.5% on re-examination (SCCS/1677/25, June 2025), both opinions excluding needle-shaped particles — cosmetics opinions about a toothpaste, not about a swallowed supplement. Swallowed microcrystalline hydroxyapatite has been trialled as a calcium source at 2 g/day. Not supported: any enamel effect from 5 mg swallowed. No such trial exists.
Read the labelHydroxyapatite is a calcium phosphate, so count it if you have been told to limit calcium or phosphate, though 5 mg is negligible against a normal diet. It is either made synthetically or milled from bone, usually bovine and sometimes fish, which matters if you avoid animal-derived ingredients, keep kosher or halal, or have a fish allergy: check the source before you buy. A chewable has to be chewed, so it is not for anyone who cannot safely chew a tablet, and not for small children. Not a treatment for tooth decay, sensitivity or gum disease, not a remineralising therapy, and not a substitute for brushing, for a fluoride toothpaste if your dentist has recommended one, or for seeing your dentist.
Evidence grades describe how well an ingredient is studied — A well-supported, C emerging — not a promise of results. Educational, not medical advice. Doses are typical ranges; follow the label on the product.