Are allergies hereditary?

Perhaps you or a family member has recently been diagnosed with allergies. You probably have many questions. One of them might be, "Did I inherit this allergy?" or "Since I'm allergic, will my children be too?".

There is a fairly large body of evidence that suggests that allergies are genetic and are passed from parent to child. However, it is not the exact allergy that is passed on, but only the tendency to have allergies.

Allergy is a defect in the immune system. The body does not correctly identify harmless proteins as benign. Instead, it tags them the same way it tags bacteria to build an immune response. So when the body misidentifies the Fel d1 protein in the saliva and urine of cats as a germ, it creates an immune response. With each subsequent exposure to this protein, the immune system mistakenly thinks it has to fight a germ. That's why allergy symptoms are so similar to a cold. Your body is fighting a bacteriological war against germs that are not there!

So the inherited defect is the tendency to misidentify the protein, but not the misidentification of a specific protein. In other words, if you are allergic to peanuts, your children can eat peanut butter sandwiches all day but can't go near a cat or dog. Your child may have seasonal allergies to pollen but you are allergic to strawberries and your grandchildren may be allergic to rabbits.

A 2024 study published in The Journal of Allergy and Clinical Immunology found that not only were allergies inherited, but they were also linked to gender. Until then, it was generally thought that allergies were maternal. That is, they were transmitted from mother to child. However, this study showed that a mother was more likely to pass on allergies to her daughter and that a father was more likely to pass on allergies to his son. In both cases, the specific allergy was not passed on (as in the previous example of peanuts and cats) but the tendency to have the allergy was passed from parent to child. This was also true for asthma and eczema.

The only exception to this general rule was penicillin allergy. If one or both of a child's parents are allergic to penicillin, it is likely that the child will be allergic to penicillin.

Similarly, studies of twins have shown that in identical twins (twins with exactly the same 25,000 genes), in more than 60% of cases, if one twin is allergic to peanuts, the other will be allergic to peanuts. In contrast, in fraternal twins (twins who share about 50% of their DNA), the rate was only 7%. So genes do play a role, but the researchers haven't yet figured out exactly what that role is.

See you next time!