Comment by Amezarak

This is common old wive's tale. Fever itself is not dangerous in adults or children.

https://publications.aap.org/pediatrics/article/127/3/e20103...

> There is no evidence that children with fever, as opposed to hyperthermia, are at increased risk of adverse outcomes such as brain damage.10,12,24–26 Fever is a common and normal physiologic response that results in an increase in the hypothalamic “set point” in response to endogenous and exogenous pyrogens.12,26 In contrast, hyperthermia is a rare and pathophysiologic response with failure of normal homeostasis (no change in the hypothalamic set point) that results in heat production that exceeds the capability to dissipate heat.12,26 Characteristics of hyperthermia include hot, dry skin and central nervous system dysfunction that results in delirium, convulsions, or coma.26 Hyperthermia should be addressed promptly, because at temperatures above 41°C to 42°C, adverse physiologic effects begin to occur.10,12,27 Studies of health care workers, including physicians, have revealed that most believe that the risk of heat-related adverse outcomes is increased with temperatures above 40°C (104°F), although this belief is not justified.7,26,28–30 A child with a temperature of 40°C (104°F) attributable to a simple febrile illness is quite different from a child with a temperature of 40°C (104°F) attributable to heat stroke.

You cannot get a dangerously high fever. You can get a dangerously high body temperature from heat stroke, or I suppose you could have some rare hypothalmic disease. But fever as an immune response is not dangerous to adults or children.