Adult-onset allergies are not unusual

DEAR DOCTOR: I’m 44 years old and have never had hay fever in my life — until this spring. I know I didn’t have a cold. Is it possible that I’ve developed an allergy?

DEAR READER: Yes, adult-onset allergies are definitely a phenomenon. From your description of your symptoms and their timing, they do sound consistent with allergic rhinitis, also known as hay fever.

An allergy occurs when an otherwise harmless substance gets flagged as dangerous by the immune system, which then launches an attack. Common allergens include pet dander, pollen, grass, mold spores, dust mites and certain proteins found in foods. The symptoms you described — itchy eyes, runny nose and sneezing — are the result of your immune system ramping up to evict the perceived intruders.

Although adult-onset allergies are not a widespread phenomenon, reports from allergists and immunologists make it clear that they are on the rise. Researchers have several theories about how and why this is happening.

One theory that has gained traction is the “hygiene hypothesis.” The idea is that in our modern world, we spend most of our time in spaces that are sealed off from the outdoors. As a result, we have very little contact with the array of plants, soils, pollens and animals in the natural world.

This results in an immune system with so little to do that it has become hypervigilant. Instead of giving harmless substances a pass, the immune response goes a little crazy and launches an all-out attack.

A different school of thought brings the body’s microbiome into play. That’s the collection of trillions of bacteria and viruses that live within the gut and upon our skin. As we are now learning, these play a surprisingly crucial role in the functioning of many systems of the human body.

This theory of how and why allergies develop views our bodies as a balanced ecosystem. The idea is that when factors like illness, pollution, poor diet or the overuse of antibiotics affect the makeup and diversity of our microbiomes, we become more susceptible to developing allergies.