How do allergies develop?

The prevalence of allergies is rising worldwide, especially among younger generations. Currently, 30-40% of the global population is expected to experience an allergic reaction at some point in their lifetime. But how did allergies emerge, and why do they exist in the first place?

While allergic reactions can be inconvenient and even dangerous, they may serve a deeper evolutionary purpose. Scientists continue to explore whether allergies developed as a defense mechanism or if they are simply an unintended byproduct of the immune system.

What are allergies?

An allergy occurs when the immune system overreacts to a harmless substance, such as pollen, dust, or certain foods. Instead of ignoring these substances, the immune system perceives them as a threat and launches a defense, leading to inflammation in the skin, sinuses, respiratory tract, or digestive system.

Although allergies may seem like a malfunction, some researchers believe they might have played a crucial role in human evolution.

The evolutionary origins of allergies

1. The hygiene hypothesis: are allergies a side effect of modern living?

One theory suggests that allergies are increasing due to reduced exposure to harmful pathogens. Modern hygiene standards, urban living, and the decline of parasitic infections mean that our immune system is less active, which could lead it to mistakenly identify harmless substances as threats.

A study published in plos computational biology found that proteins in common allergens, such as birch pollen, closely resemble proteins found in parasites like schistosoma mansoni—a type of flatworm. The same antibodies that respond to parasite proteins also react to allergens like pollen, indicating that allergies may have evolved due to the immune system’s lack of exposure to real threats.

In simple terms, when there is no real danger, the immune system may create one.

2. Are allergies an evolutionary defense against toxins?

Another theory, supported by studies in scientific american, suggests that allergies are not a coincidence but rather a survival mechanism that protects against toxins in the environment.

To test this, researchers exposed mice to small doses of venom before later introducing them to highly toxic levels. The mice that had previous exposure showed a much stronger immune response, producing allergen-specific antibodies that prepared them for future threats.

This suggests that allergic reactions may act as a warning system, helping the body recognize potentially harmful substances and respond before they cause serious harm.

For example, symptoms like vomiting, difficulty breathing, or skin reactions may have historically helped humans avoid dangerous plants, insect bites, or spoiled food.

What do these theories mean for us today?

• If the hygiene hypothesis is correct, allergies may have emerged as an unintended consequence of modern sanitation and reduced exposure to natural pathogens.
• If the toxin-defense hypothesis is true, allergies may have originally developed to prepare the body for dangerous encounters.
• Both theories suggest that small allergic reactions could "train" the immune system to recognize and react to real dangers more effectively.

The mystery of allergies continues

Despite ongoing research, the true origin of allergies remains unknown. Some scientists believe allergies serve an evolutionary purpose, while others argue they are simply a result of the immune system misfiring.

What is certain, however, is that allergies are becoming more widespread, affecting millions of people worldwide. Understanding their development may not only help manage allergic reactions but could also unlock new insights into immune system function and human evolution.

For now, the question of why allergies exist remains one of nature’s greatest medical mysteries.