From a physiological perspective, "spiciness" is a sensation of pain. However, this pain is enjoyed by many people. Everyone's tolerance for "spicy flavors" varies, but spiciness that exceeds an individual's tolerance can cause discomfort. So, if you get "spicy-hot" — whether it's in your mouth or on your hands — what methods can effectively alleviate that "fiery" feeling?
The substance responsible for the "fiery" sensation is called "capsaicin," also known as "capsaicinoid." It is highly hydrophobic, meaning it does not dissolve in water and has a waxy consistency. In the human mouth and on the skin, there are specific nerve receptors. When capsaicin binds to these receptors, it generates corresponding nerve signals that are transmitted to the brain, resulting in the perception of "spiciness."
When we feel "fiery," the capsaicin has already bound to the nerve receptors. To alleviate this uncomfortable sensation, we need to dislodge the capsaicin from the receptors and prevent it from binding to others. Since capsaicin is not soluble in water, it’s understandable that water isn’t an effective way to "quell the spiciness."
Someone organized over 20 volunteers to experimentally compare the effectiveness of different "anti-spicy" methods. The results showed that after being exposed to spiciness, rinsing with water had some effect, and ice-cold water was more effective than room-temperature water. However, when compared to milk, milk proved far more effective. The reason may be that milk contains large amounts of casein, which is an excellent emulsifier capable of efficiently encapsulating and carrying away hydrophobic substances. The study further found that different types of milk did not vary much in effectiveness, but temperature had a greater influence. Overall, cold whole milk worked best.
This study also tested the "anti-spicy" effects of sucrose water. A 10% sugar solution had an effect comparable to milk at 5°C. For those who dislike or cannot consume milk, this might be good news. As for why sugar water can reduce the "spicy" sensation, scientists have proposed various hypotheses without sufficient evidence to prove them. However, for us, knowing that "sugar water alleviates spiciness" is enough.
Theoretically, alcohol should dissolve capsaicin and thus have good anti-spicy properties. This aforementioned study also compared the "anti-spicy ability" of alcohol. They used a 5% alcohol concentration, roughly between beer and wine. Surprisingly, this concentration was no more effective than room-temperature water. However, other sources suggest that 20% alcohol concentration would be highly effective. Considering this concentration is equivalent to low-alcohol liquor, using it to "alleviate spiciness" doesn't seem like a great choice. Of course, if your hands are "spicy-hot," washing them with alcohol could be a good solution.