Are twins allergic to the same things?

If one twin is allergic to something, does that mean the other will be too? Allergies — whether it’s spring sneezes from pollen or trouble breathing after eating certain foods — are influenced by a mix of genetics and environment. The more these factors overlap between two people, the higher the chances they’ll share the same allergies. Since twins share so much, they’re more likely to have similar allergies, but studies show that it’s not guaranteed.

Allergies can sometimes trigger anaphylaxis, a severe, life-threatening reaction that requires immediate medical attention. An article by the BBC looking into this question points out that signs include throat swelling and rashes after exposure to an allergen. The standard treatment for anaphylaxis is an injection of epinephrine (also called adrenaline) into the leg muscle. Allergy sufferers often carry auto-injectors for emergencies, and now a fast-acting epinephrine nasal spray is available too.

People can be allergic to outdoor triggers like grass, tree pollen, and bee stings, or indoor ones like pet dander and dust mites found in carpets and mattresses. Each allergy is highly specific because antibodies target particular allergens. Interestingly, the same antibodies that cause allergies also defend against parasites — a task they rarely perform in modern environments, which may explain why they sometimes "misfire" at harmless things like food or pollen.

Studies show that identical twins (who share 100% of their genes) are more likely to have the same allergies than fraternal twins (who share about 50% of their genes, like regular siblings). An Australian study found that 60%–70% of twins shared environmental allergies. Research into food allergies, like peanut allergies, also shows a stronger link among identical twins.

However, sharing genes doesn’t guarantee identical allergies. Environment plays a big role too. If twins are raised in very different settings — say, one on a farm with animals and the other in a city apartment with smokers — their allergy profiles could turn out very different. Some might develop allergies, and others might not.

The article points out that our immune system’s job is to defend us from harmful invaders. It makes antibodies that recognize and attack germs. But sometimes it mistakes harmless substances — like pollen or peanuts — for threats. When that happens, antibodies latch onto the allergens and trigger an immune response, causing symptoms like sneezing, a runny or stuffy nose, itchy, watery eyes, and coughing. While annoying, these symptoms are often mild — unless they escalate to more serious reactions like anaphylaxis.

By Nazrin Sadigova