When one twin develops an allergy, it’s natural to wonder if their sibling will suffer the same fate. According to experts, the answer isn’t straightforward — while genetics play a major role, environment and lifestyle are just as important.
Allergies, whether to pollen, food, or dust, are caused by a mix of inherited genes and environmental factors. Since twins often share both, they are more likely than unrelated individuals to have similar allergic reactions. However, researchers say it’s not a guarantee.
An allergy occurs when the immune system mistakes a harmless substance for a dangerous invader, triggering an immune response. This leads to symptoms like sneezing, itchy eyes, and coughing. In severe cases, allergies can cause anaphylaxis — a life-threatening condition that requires immediate treatment, often with an injection of epinephrine or a fast-acting nasal spray.
Allergies can stem from various sources, including outdoor triggers like pollen or bee stings, indoor irritants such as pet dander and dust mites, and certain foods. Food allergies, affecting about 4% to 5% of the population, are most common with items like peanuts, shellfish, and dairy products. Some people outgrow their allergies; others live with them for life.
Environmental exposure is another key factor. Studies show that children raised on farms, those with pets, or those breastfed as infants have lower allergy risks. In contrast, city living, pollution, and second-hand smoke increase the chances of developing allergies. Early exposure to a variety of foods has also been shown to reduce the risk of food allergies in children.
Genetics, however, remain a strong predictor. Children of allergic parents are significantly more likely to develop allergies themselves. In fact, if a parent or sibling is allergic to peanuts, the likelihood of a peanut allergy is about seven times higher.
When it comes to twins, genetics matter even more. A study in Australia found that between 60% and 70% of twin pairs both had environmental allergies. Identical twins, who share 100% of their genes, were more likely to have matching allergies than fraternal twins, who share roughly 50% of their DNA, just like typical siblings.
While twins often have much in common, their allergy profiles can still differ, influenced by a lifetime of individual experiences. The research highlights the complex interplay between our genes and the environments we grow up in — making each person’s immune system truly unique.
