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Allergies affect millions worldwide, from seasonal sneezing to severe food reactions. Researchers are now uncovering how both genetics and environment contribute to allergy risks, particularly in twins. Studies show that the more twins share genetics and early experiences, the more likely they are to have similar allergy sensitivities. However, the story is far from simple. Other factors also play a role in whether an individual develops allergies or not.

How Allergies Develop in the Body

The immune system plays a critical role in protecting the body from harmful invaders like germs. It produces antibodies that target these threats. However, when the immune system mistakenly identifies harmless substances like pollen or pet dander as dangerous, it triggers an allergic reaction. This reaction causes common symptoms such as sneezing, itchy eyes, a runny nose, and persistent coughing. In rare cases, allergies can lead to anaphylaxis, a severe, life-threatening reaction that requires immediate medical intervention, typically through an epinephrine shot.

Food Allergies and Other Common Triggers

Food allergies affect a significant portion of the population, with 4% to 5% of people experiencing reactions to common allergens like milk, eggs, peanuts, and shellfish. While some people outgrow these allergies, others live with them for life. Allergens are also found in many environments, both indoor and outdoor. Pollen, pet dander, and dust mites can be common indoor allergens, while bee stings and mold are common outdoor triggers.

What Determines Who Develops Allergies?

Each individual’s immune system produces specific antibodies that react to certain allergens. Research suggests that hygiene and a lack of exposure to parasites in modern, industrialized countries might increase allergy risks. In these environments, antibodies, which typically protect the body from parasites, sometimes react to harmless substances instead. Children who grow up in more rural environments, on farms, or with multiple siblings are generally less likely to develop allergies, as early exposure to bacteria helps strengthen their immune systems. On the other hand, urban children tend to face higher allergy risks due to factors like air pollution and cigarette smoke.

The Role of Family History

Family history plays a significant role in allergy development. If a child’s parents or siblings have allergies, that child is more likely to develop them as well. In fact, the risk of developing peanut allergies increases sevenfold if an immediate family member has the same sensitivity.

Do Twins Share the Same Allergies?

Research from Australian scientists shows that 60% to 70% of twins share environmental allergies. Identical twins, who share the same genetic material, are more likely to have similar allergies compared to fraternal twins, who only share about half of their genes. This tendency is also reflected in food allergies, such as peanut allergies. A study found that identical twins were more likely to both have peanut allergies than fraternal twins.

However, this doesn’t mean that all twins will develop the same allergies. While genetics certainly play a large role, environmental factors such as where and how a twin grows up also have a significant impact. For example, one twin who grows up in a rural area with pets and siblings may be less likely to develop allergies than another twin who lives in an urban environment with higher levels of air pollution.

Why Environment Matters

Even with identical genetic makeup, twins exposed to different environments may experience differing allergic reactions. For instance, one twin may grow up on a farm with clean air and many pets, while the other may live in a polluted city with few animals. The twin in the cleaner environment might not develop allergies, while the one in the city could face challenges due to higher pollution levels and fewer natural exposures to bacteria.

The Continuing Research

Researchers continue to investigate how genetics and environment combine to shape allergy risks. Studies are shedding light on how early life experiences, family history, and exposure to different environmental factors contribute to allergic conditions. By understanding these complex interactions, scientists hope to find better ways to manage and even prevent allergies in the future.