Summer-Heat is a Yang Pernicious Influence and, as such, it tends to injure Yin. This Pernicious Influence is different from the five others in two ways: first, it is definitely related to a specific season since it can only occur in the Summer; secondly, it can be only an external pathogenic factor with no internal equivalent.
Overexposure to Summer-Heat causes profuse perspiration and then exhausts Qi and Body Fluids. It is usually accompanied by Dampness since it can be caused by hot-humid climates or Heat reacting to the body's Damp-Heat environment. In this case, both the Heat and Dampness must be treated.
The possible symptoms are:
Summer-Heat invades the Exterior of the body and that is why there is aversion to cold (even though the exterior Heat is intense). However, it has the strong tendency to move to the Qi level and that is why there are symptoms of interior Heat such as irritability, thirst, Red tongue and Rapid pulse.
In severe cases, Summer-Heat can invade the Pericardium and cause clouding of the mind, manifesting with delirium or unconsciousness.
Summer-Heat is a Yang pathogenic factor and therefore it has a strong tendency to injure Yin (i.e. to injure fluids).
Summer-Heat can occur only in the Summer and it can be only external (i.e. contrary to other external pathogenic factors, there is no internal equivalent).
Summer-Heat invades the top of the body and for this reason there is a headache.
The scattering nature of Summer-Heat causes sweating.
Summer-Heat often harbours Dampness and, for this reason, there is a feeling of heaviness a feeling of nausea / an uncomfortable sensation of the epigastrium.