Peppermint can make your mouth feel cold even when the mint itself has been sitting at room temperature.
The trick comes from menthol.
Menthol activates temperature-sensitive nerve receptors that normally respond when tissue cools.
Your brain receives a cooling signal even if the actual temperature changed very little.
Your nerves have temperature sensors
The body uses specialized proteins to detect potentially important temperature changes.
One of these is called TRPM8.
It responds to cool temperatures.
Menthol can also activate it.
That means the same signaling pathway can turn on because the tissue became colder or because menthol arrived.
Why does toothpaste feel cold?
Many toothpastes, gums, candies, and mouthwashes contain menthol or mint-derived flavor compounds.
When menthol reaches sensory nerves in the mouth, the cooling pathway becomes active.
The bathroom did not suddenly drop ten degrees.
Your nervous system changed its report.
Why does cold water feel extra cold after mint?
The receptor is already being stimulated by menthol.
Then genuinely cold water adds a real temperature change on top of the chemical signal.
The combination can make the cooling sensation feel especially strong.
This is why a sip of ice water after strong mint can feel almost aggressively cold.
Is mint lowering the temperature at all?
Sometimes evaporation and airflow can produce small real cooling effects, but the characteristic mint sensation does not require a dramatic temperature drop.
Menthol can create the feeling even in otherwise warm surroundings.
Is menthol the opposite of capsaicin?
In a useful everyday sense, they pull opposite sensory tricks.
Capsaicin activates pathways associated with heat and burning.
Menthol activates a pathway associated with cooling.
Neither chemical needs to change the temperature enough to match the sensation.
Your nerves are reporting how their receptors were activated, not reading a thermometer.
Why does mint feel refreshing?
Humans generally associate cool sensations with freshness and relief from heat.
That makes the menthol effect useful in foods and personal-care products.
The chemical signal becomes part of the flavor experience.
So peppermint is not carrying a little air conditioner around inside the leaf.
It is convincing your nerves that somebody turned the thermostat down.
A related bit of kitchen science appears in Why do chili peppers feel hot?, where a different familiar food has its own chemistry.
And that’s the short explanation.
Related explanations: Why do chili peppers feel hot?, Why does soda fizz?, and Why does metal feel colder than wood?