Have you ever drunk hot water? I once did on a cold day, thinking that it would feel much better than an ice-cold glass. To my dismay, it did little to quench my thirst and dry throat. In fact it did the opposite – it gave me the odd sensation of a dry mouth.
If you do not know what I am talking about, then go now and have a cup of hot water. You will be as surprised as I was. Now, why is this?
Your mouth cavity is covered by a layer of saliva. This saliva has some amazing properties. Most obviously it prevents your mouth from drying out, and helps to soften food. However within the saliva there are many chemicals that assist in many ways. For example, there are enzymes within saliva that help digest carbohydrates (amylase) before the food enters the stomach. In addition the saliva helps to keep the pH of the mouth neutral, so despite what food we eat, whether acidic like an orange or alkaline like a nice cup of tea, the pH in our mouth will remain constant. Furthermore, the saliva contains essential minerals to keep the enamel on our teeth strong, but whats more the neutralising properties of saliva helps prevent tooth decay. Finally the saliva contains antibodies from our immune system which help to fight infection – which could be why many animals tend to lick their wounds when hurt.
So this is why our saliva is so important. Since it is such a crucial part of our mouths, it is always there. Saliva feels wetter than water. When you drink hot water,the saliva is washed away leaving just a thin layer of water. Until your salivary glands produce enough saliva, your mouth will feel noticeably dryer than before.
However, cold water may not have as much of an effect because it is less likely to dilute the saliva layer. Additionally it numbs the nerves in your mouth, meaning you don’t detect the dryness as much.