Why Mammals Are Naturally Resistant to Many Fungal Infections

Mammals resist many fungal infections partly because their high body temperature blocks many fungi from growing, creating a natural thermal barrier.

Medicine

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Mammals have an unusual defense against many fungi that does not require the immune system to attack the fungus directly: body temperature itself can make the body a difficult place for fungi to grow. Most fungi grow best at temperatures well below typical mammalian temperatures, and studies of thousands of fungal strains found a sharp decline in the number able to grow as temperatures rise above about 30 degrees Celsius. This creates what researchers describe as a thermal exclusion zone around the normal body temperature of mammals. A 2010 model found that the balance between the metabolic cost of maintaining a warm body and the benefit of restricting fungal growth peaked near 36.7 degrees Celsius, close to typical mammalian temperatures. The idea is that endothermy may therefore have provided mammals with an important advantage against environmental fungi. It is not established that mammals evolved warm bodies specifically to fight fungi, because endothermy has many other benefits and its evolutionary origin is still debated. Healthy mammalian immune systems add another major layer of protection, which helps explain why serious invasive fungal disease is uncommon in otherwise healthy people. This protection is not absolute: superficial fungal infections such as athlete’s foot are common, and some fungi have evolved enough heat tolerance to infect mammals. The thermal barrier is best understood as one part of a broader defense rather than a complete shield.

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