Dear Doctor:

I’m 44 years old and have never had hay fever in my life. This spring, just as everything was turning green and the flowers were blooming, my eyes started to itch, my nose was running, and I was sneezing all the time. I know I didn’t have a cold. Is it possible that I’ve developed an allergy?

Dear Reader: We regret being the bearers of bad news, but 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, but a definitive answer is not yet known.

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. It’s not that the immune system has become ineffective, but rather it has developed reactions that are inappropriate and are out of proportion to the perceived threats.

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.

A definitive answer may one day point to new ways to manage or even “cure” allergies. But until then, we’ll rely on what we already know.

First, we recommend that you see your primary care physician for a definitive diagnosis. Hay fever symptoms can be managed with antihistamines or decongestants, which your physician may recommend. And limiting exposure — staying indoors during peak pollen season, using air conditioning instead of fans, investing in an air purifier and wearing sunglasses can help make this new (again, we’re so sorry) allergy more bearable.