Are twins allergic to the same things?

If one twin is allergic to something, does that mean the other twin will also be sensitive?

Allergies, whether it's spring sneezing due to pollen or breathing problems triggered by a certain food, are caused by a combination of someone's genes and the environment they live in. The more of these things two people share, the higher their chances of being allergic to the same things.

Twins are more likely to share allergies because of everything they have in common, but the story doesn't end there.

Allergies are really complex and many factors play a role in who gets them and who doesn't.

What is an allergy?

Your immune system produces protective proteins, antibodies, whose job is to watch for and attack any invading microbes or other dangerous substances that enter your body before they can make you sick.

An allergy occurs when your body mistakes some normally harmless substance for a harmful intruder. These triggering molecules are allergens. Antibodies attach themselves like suction cups to the allergens, triggering an immune system reaction. This process leads to common allergy symptoms: sneezing, runny or stuffy nose, itchy, watery eyes, and coughing. These symptoms can be bothersome but minor.

Back to the idea of ​​twins: yes, they can be allergic to the same things, but not always.

Researchers in Australia found that 60% to 70% of twins in one study both had environmental allergies, and identical twins were more likely to have allergies than fraternal (non-identical) twins. Identical twins share 100% of their genes, while fraternal twins share only about 50% of their genes, just like any other pair of siblings.

Much more research has been done on the genetics of food allergies. One study of peanut allergy found that identical twins were more likely to both be allergic to peanuts than fraternal twins.

So, twins can be allergic to the same things, and are more likely to be allergic, based on their shared genetics and growing up together. But twins are not automatically allergic to the same things.

Imagine if two twins were separated at birth and raised in different homes: one on a farm with pets and one in the city center. What if one's parents smoked and the other didn't? What if one lived with many siblings and the other was an only child? They would likely develop different allergies, or perhaps no allergies at all.