For some who have moved from tropical to non-tropical countries for the first time, the changing of the seasons comes as a welcome surprise, with the fantastic colors, growth of new vegetation and changes in daylight duration. 

For others, the vibrant burst of nature that is spring has come to represent something a little less beautiful: Hay fever. 

Achyut Shanker first came to Germany in August 2022. In his hometown, New Delhi, he’d never experienced allergies, he told DW. The management consultant is currently completing a master's degree at the Hertie School in Berlin.

"I never had this feeling there [New Delhi] … when I came here [Berlin] last year, that's the first time when I had it,” said Shanker.

So what causes these new allergies in people who have never experienced anything like it before?

What is hay fever?

Believe it or not, hay fever has nothing to do with hay, and fever is not a common symptom.

The condition is also known as “seasonal allergic rhinitis”. Think of rhinoceros, "nose-horned” — "rhin" or "rhino" means nose and "-itis" means inflammation. 

Hay fever is caused by an allergic reaction to something your body detects as foreign. In this case, that substance is pollen, which is essentially microscopic plant sperm. 

When does it occur?

"First time I felt it was in September only. And then again in February and again in April,” said Shanker.

Hay fever happens during times of the year when certain plants release their pollen — hence the seasonal aspect. In spring, trees like birch produce the most pollen in northern and central Europe, acting as the main source of hay fever, according to this study.

During summer, it's mostly grass, while in the fall, it's usually weeds, like ragweed.

There is no cure, although its symptoms can often be managed with medication, like nose sprays and antihistamines.

"The medicines that they gave here were not really helpful,” said Shanker. He instead opted for washing his nose with salt water every morning.

Allergies are strange

Allergies are complicated. Some people have them, some don't. Some develop them later, others are allergic to very specific things. It's still not entirely understood why they appear in such a wide range. Overall, it has to do with genetics, your immune system and the environment. 

Moving to a new environment or climate, for example, can expose you to new substances that cause allergies — technically called allergens.

Some studies suggest that playing and getting dirty in nature while growing up may help reduce the risk of developing allergies later in life.

A big toll on quality of life

Although one might not think allergies are that much of a deal, conditions like hay fever go way beyond a runny nose. "For me, I think it was more that it would drain my energy. I would feel very low and like I had no energy or motivation to get up and go to university," said Shanker.

Hay fever can cause annoying symptoms, like constant sneezing. "One night, I was counting, I sneezed almost 25 times in a row," Shanker said.

It can cause a puffy feeling in the face, a blocked nose, very itchy eyes and coughing. It can also trigger asthma symptoms in people with allergic asthma. 

These symptoms — especially when combined — can change your mood, affect your sleep and make it harder to focus, according to the American College of Allergy, Asthma & Immunology.

In Europe, around 40% of people are allergic to pollen, making it the most common source of allergies, according to the European Climate and Health Observatory. And it is likely to increase with climate change, which is prolonging and intensifying pollen seasons. Not great news for people like Shanker.

When the immune system overreacts

Some people think allergies are due to a problematic or weak immune system, but experts say that’s a myth. 

"This will surprise many, but allergy sufferers actually have a better immune system,” said Torsten Zuberbier, allergology professor at Charite Hospital, in an interview with WELT.

Ok, a good immune system — that’s not so bad. The problem is that it overreacts. It goes into overdrive when harmless, microscopic pollen grains reach your nose or eyes. Your immune cells detect them and yell "attack", triggering an immune response.

People with hay fever often take antihistamine medications. That’s because when pollen enters the body of someone with allergies, their immune system causes a spike in the production of histamine, a chemical that tells your body something potentially dangerous has entered that needs to be got rid of.

In response, you sneeze, itch and your eyes water. Inflammation can also occur. Antihistamine medications are designed to block this response. 

That's the case with every allergic reaction, not just hay fever.

Pollen is everywhere

The thing is, this wasn’t the first time Shanker had been exposed to pollen. "Even a city like Bangalore is known for pollen, but when I went there for a couple of days, I didn't feel it," he said.

Indeed, pollen is basically everywhere — it's how seed plants reproduce. The flying sperm makes its way onto the flowers' so-called "female" structure, the pistil. The pollen fertilizes in ovules in order to develop into a seed, and with some luck, grow into a plant. So wherever there are plants that produce seeds, there is pollen.

Like fruits, pollen differs by geographic region — mangos don’t grow in Germany, for example. There are many microscopic differences in the pollen of plants, based on where they grow.

The size of an individual pollen grain ranges from around two to 100 micrometers. That's taking a millimeter and dividing it into a thousand parts — don't try it at home, it might take a while. 

Different pollen grains around the world

For people like Shanker, this vast diversity of pollen could be the reason behind newly acquired allergies.

Just as some people can be allergic to just a few types of food, like peanuts or apples, allergies to pollen can vary based on the individual type of grain. And the pollen grains that are common in Europe are not the same as those in, say, India.

"When I spoke to other Indian students, many of them were complaining about the same thing [hay fever]," he said. 

Some studies have confirmed this phenomenon, showing that migrants are more prone to seasonal allergies. 

Edited by: Clare Roth