The cooling sensation of skin can be roughly divided into four mechanisms:
- The first is to absorb heat through evaporation of volatile components, taking away a large amount of heat from the body to achieve the effect of physical cooling.
For example, ethanol as the solvent of toilet water, propane and butane as spray propellants, etc., achieve the purpose of instant cooling or balancing the oil sense through high volatility. However, it should be noted that the flash point and ignition point of ethanol, propane and butane are very low, so it is necessary to avoid high temperature and open fire to prevent accidents. At the same time, such products also have certain restrictions when taking public transportation such as aircraft and high-speed rail.
- The second is to use substances with high dissolution heat.
For example, when erythritol is dissolved in water, it will absorb a lot of heat and has a good cooling and refrigeration effect.
- The third is to use the high specific heat capacity of water.
For example, when the prepared medical cooling hydrogel products are in contact with the skin, due to the temperature difference between the skin and the gel, heat exchange will occur, resulting in the decrease of skin temperature, while the hydrogel temperature increases, and the increase of hydrogel temperature will accelerate the water evaporation inside the gel, and the water evaporation will take away a large amount of heat, further reducing the temperature. Water evaporation is a slow process, which can play a continuous cooling and cold compress analgesic effect.
- The fourth is the realization of "deception" neurosensory.
For example, menthol and borneol act on the TRPM8 ion channel of the temperature sensor, allowing ca2+ to enter the cell in a non low temperature environment, and "deceiving" the human nerve to sense a cool experience similar to cooling. The mechanism of action is shown in the figure.
Although menthol is a traditional herbal cooling agent, it also has certain limitations in the application of cosmetics. For example, it has a strong Mint smell, which is not easy to cover up and affects the flavor of the product; Volatile, not suitable for high-temperature production process; It has the effect of promoting permeability and has certain irritation to mucosal tissues. It needs to avoid wounds and sensitive muscles; Although the cool feeling is strong, it is also short-lived. Because of these shortcomings, menthol derivatives came into being, such as menthol lactate, menthol glycerol ketal, menthol PCA, etc., which can reduce the irritation and odor of menthol to a certain extent, improve the cool durability, and be more mild and efficient.
Among the four mechanisms, the first three have substantial temperature lowering effects. The first two are instant cooling, with a weak sense of cooling duration and need to be applied intermittently. The latter takes away the body surface heat due to the evaporation of water, with a strong sense of cooling duration; The fourth kind will not substantially reduce body temperature. It is the cool feeling "felt" through nerve sensing. Combining two or more mechanisms will bring more obvious synergy.
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