An oral temperature above 98.6 degrees Fahrenheit but below 100.4 degrees Fahrenheit is a low-grade fever. A fever can be symptomatic of many conditions, and the low-grade variety is often not cause for concern. However, any fever that persists for more than 24 hours warrants a doctor visit if the cause is undetermined.


1. Allergies

Allergies trigger the release of a chemical called histamine, which the body unleashes to attack substances it deems irritating or injurious. Histamine affects the hypothalamus, a region of the brain that is responsible for regulating body temperature, which is why allergies induce a low-grade fever in some people.

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