Getting thermal comfort by cooling just one point of body? Can I get thermal comfort by cooling or heating just one point of body like wrist or foot?
As far as I know, Wrist and foot are the most thermally sensitive points of body. I saw that wrapping a wet cloth in the wrist can give someone thermal comfort during summer. Is it really effective? If it is really effective, where should I wrap wet cloth between foot and wrist to get more cooling effect?
 A: Most definitely, yes you can cool your whole body by cooling only a small region for a very clear reason: the human vascular system (the same can be said for any animal with a heart-pumped circulatory system).
Heat flows through conduction out of the blood in the locally cooled region into whatever is cooling it - the ice pack, or the skin cooled  evaporatively / convectively. Then this slightly cooled blood is pumped to all other parts of the body; heat can then be conducted from other body parts into the blood. The cycle repeats, so the blood is constantly ferrying heat through conduction from throughout the body to the locally cooled region.
Indeed, this principle is also widely used in industry for the disposal of waste heat or transfer of heat to where it is needed. Coolant is often cooled by cooling towers and then pumped through the industrial plant whence we want to dispose of heat - the heat to be disposed of is generated remotely from the cooling tower. Likewise, a liquid sodium "vascular system" is used to transfer heat from the core of a nuclear reactor to the remote heat exchanger, where it is cooled through the production of steam for turbines and the attendant loss heat to supply the latent vaporization heat for the water. 
A: They tell boy scouts on hikes:

If your feet are cold, put on your hat.

The explanation: your bare head loses a lot of heat and your body compensates by reducing blood flow to hands and feet, which can tolerate reduced temperatures (that would be detrimental to the brain or internal organs).
So, yes to the heating part (if reducing heat loss is equivalent to heating).
A: yes, there are products such as wrist bracelets that use the fact that your blood vessels are close to the surface on the wrist.
Search for "wrist cooling device"
They seem to be active, using e.g. Peltier effect.
There was an article about a device that uses a closed water circuit and was at least tested for tennis players. The method is apparently effective, I am not sure how safe it is though.
