pH, mint and the nicotine pouch burn
The sensation under the lip is not the same as nicotine content. pH, free nicotine, moisture, pouch material, salt, flavourings and contact time all influence the experience.
pH and free-base nicotine
Higher pH normally increases the fraction of uncharged free-base nicotine that crosses oral mucosa more readily. This can speed absorption and may feel harsher or more tingling, but pH alone does not determine sensation.
Mint, menthol and cooling agents
Menthol and cooling agents activate receptors including TRPM8. Lower concentrations can feel cooling and may reduce irritation, while higher concentrations can themselves irritate or burn. It is therefore too simple to say mint always burns more than strawberry.
Sensory “burn” must not be used as a proxy for nicotine content.