The classic 'sensitive teeth' ingredient. It calms the tooth nerve over a few weeks of twice-daily use; the benefit is real but moderate.
Tooth sensitivity happens when exposed dentine lets cold, air or touch reach the nerve through tiny tubules. Potassium ions diffuse along those tubules and damp down nerve firing. It does not block the tubules, so relief builds gradually and fades if you stop.
Most desensitising toothpastes use 5% potassium nitrate, usually alongside fluoride.
An older Cochrane review of six small trials found reductions in measured sensitivity but not in patients' own ratings and called the evidence unclear. Larger network meta-analyses since (125 and 32 trials) found potassium pastes beneficial with moderate certainty, especially for touch-triggered pain, with stannous fluoride and some other agents at least as effective.
Six small trials: potassium nitrate paste reduced sensitivity to air blast and touch at 6-8 weeks, but patients' own ratings did not improve significantly; the authors judged the evidence insufficient for clear support.
125 RCTs (12,541 patients). Compared with ordinary fluoride paste, stannous fluoride, potassium salts (alone or combined with stannous fluoride), calcium sodium phosphosilicate, arginine and strontium reduced sensitivity to at least one stimulus, with moderate-to-high certainty.
32 trials (4,638 adults) with standardised methods: twice-daily toothpastes containing stannous fluoride, potassium with or without stannous, or arginine can be recommended to reduce sensitivity pain.