WHY MOSQUITO BITES ITCH

When female mosquitoes insert their proboscis through your skin to suck some of your blood to be later used to make eggs, they inject you with some of their saliva. Their saliva helps them to drink your blood more quickly, because it has anticoagulant effect (for your blood not to clot). Once the female mosquito is full up of your blood or is disturbed by slapping yourself, they fly away, leaving some of their saliva behind. Your body responds by producing antibodies which bind to the antigens in the mosquito's saliva. This then triggers  the release of histamine.

Histamine is a nitrogen compound that, among other things, triggers an inflammatory response. It also help white blood cells and other proteins to engage invaders (antigens) in your body by making the capillaries of these cells more permeable. So, the histamine ends up making the blood vessels near the bite site swell up. This produce a itchy bump where the mosquito bite you.

Scratching the bump only makes this worse because it causes more irritation and inflammation of the sight, resulting in your immune system thinking it needs more antibodies to get rid of the foreign protein. So the more you scratch, the more it swells and the itchier it gets.

*Only female mosquitoes feed on blood, a male mosquitoes feeds on flower nectar or sweet juices.

WHY IT IS NEARLY IMPOSSIBLE TO TICKLE YOURSELF

It's very hard to tickle yourself because your brain anticipates things going on around you in order to help speed up response times. More technically, the cerebellum monitors body movements and can also distinguish between expected sensations and unexpected ones, generally resulting in diminishing or completely discarding expected sensations, while paying much more attention to unexpected ones

So your brain is actively anticipating touch sensations. When it is doing this, it is also actively discarding sensation that it deems unimportant, like when you are typing and it significantly dulls the touch sensation in your fingertips so that you don't really notice it unless you consciously think about it. This same type of thing happens when you try to tickle yourself.

So in a nutshell, you can't usually tickle yourself because there is no element of surprise.

WHY MINT TASTE COLD

There is a chemical in mint, menthol, which is deceiving the brain into thinking that the area the menthol is applied to is cold; even though in fact, it's the same as it was before. More specifically, menthol binds with cold-sensitive receptors in your skin; there receptors contain things called "ion channels", in this case TRPM8. The menthol makes these much more sensitive than normal, so they trigger and you feel a cold sensation, even though everything is more or less the same temperature as before.

This extra sensitivity is why when you eat peppermint, which has a relatively high level of menthol, and then you breathe in deeply through your mouth, your mouth feels extra cold. Your cold receptors are reacting much more strongly than they normally would to the air which is cooler than the inside of your mouth.

Menthol is a compound classically obtained from various mint plants, though now is oftern synthetically made due to the extreme high demand for menthol in a variety of products. Menthol is a waxy, crystalline substance that is somewhat clear or white. Interestingly, it is actually solid at room temperature and melts just a few degrees above room temperature.