Peppermint Or Spearmint For Fever?

Plants and hence , essential oils made from them have their unique characteristics (like the conditions they prefer to grow) and physical properties.  For example, we can use peppermint to lower the fever when needed (caution - do not use it over big body areas, as it may bring the body temperature too much down).  

Peppermint is also a hot oil (we may dilute 1 drop of it with 4 drops of vegetable oil).  Peppermint may cause sweating thereby assisting your body in cooling.  Spearmint does not cause sweating and would be more beneficial when a person has a fever without chills (Dennis Willmont, Aromatherapy with Chinese Medicine)

This is just one property of these essential oils. Each essential oil, if it is of a high quality, has many constituents and therefore assist the body in many ways in balancing itself.