The neck and face feel quite hot and there may be heart palpitations, sweating, dizziness, headaches and anxiety.
The face turns red.
It may last from a few seconds to an hour.
The severity of the symptoms may range from mild to severe.
Most of the sufferers of hot flashes are women undergoing menopause - about 75% of them.
Some men on the controversial andropause, men on hormone restriction therapy for prostate problems, persons with hyperthyroidism, low blood pressure and low blood sugar are also prone to hot flashes.
The mechanism of hot flashes is simple.
The blood vessels on the neck and head enlarge and allow more blood than normal to pass.
This gives the hot feeling and causes other symptoms.
The cause of the blood vessels' dilating is still unknown.
In menopausal women the hormone level is related to the hot flashes.
It is not the level of hormones per se, but the wild fluctuations in the level, that seem to trigger the attack.
There are no proven approaches to connect the fluctuations of hormonal levels and the dilation of blood vessels.
The mid-brain hypothalamus gets confused, when the hormone levels are fluctuating, and orders the dilation of blood vessels to get rid of the non-existent extra heat.
The temperature of the skin on the neck and head rise suddenly and sharply.
This gives the feeling of heat.
As the hot flash passes, there is a chilling of the body, further confirming that the thermostat on the brain is confused.
In response to hormonal fluctuations, the pituitary gland may also be releasing its own hormones to dilate the capillaries and cause them to increase blood flow.
There is also a view that psychological factors, such as stress and anxiety, play a part in hot flashes, or at least in triggering one.