What Causes Seasonal Allergies?

Seasonal allergies, like other types of allergies, develop when your body’s immune system detects and then overreacts to a foreign substance it thinks is harmful. And the symptoms you experience like sneezing and a runny or stuffy nose are your immune system’s way of fighting off the invader.


Pollen is a common cause of seasonal allergies. Pollen is a powdery substance produced by trees, grasses and weeds as part of their reproductive cycle. It’s lightweight and dry, so traveling long distances in the wind is easy. A high pollen count means you’re much more likely to have worse allergy symptoms. Many TV weather broadcasts now include a report on the pollen count in your area.


Mold typically appears as black, white or green splotches on damp surfaces. It commonly grows in bathrooms and basements, but outdoor culprits include soil, fallen wet leaves and plants.

Like pollen, mold spores are carried through the air. But unlike some allergens, mold easily travels on both wet and dry days.

Dust mites

Dust mites are microscopic bugs that live in warm and humid environments. Their skin droppings – not bites – are what cause an allergic reaction.

Dust mites like bedding, carpet, stuffed animals and furniture. So, if you have a dust mite allergy, you can have allergy issues throughout the year.

Animal dander

Contrary to what many people may think, animal fur or hair alone doesn’t cause allergies. It’s the animal’s dander – which are skin flakes they’ve shed – that usually triggers allergies. That’s because dander, along with saliva and urine, contain proteins that can cause an allergic response.


Some people can suffer from allergy symptoms when they breathe the air around dead cockroaches and cockroach droppings.

When is allergy season and how long do seasonal allergies last?

Actually, there isn’t just one allergy season. Instead, there are certain times during the year when allergy symptoms may be more severe, depending on what you’re allergic to.

As for when allergy seasons start and stop, it depends on where you live. If you have indoor allergies, you could experience allergy symptoms year-round – including in the winter. But generally, there are three seasons when outdoor allergens trigger annoying symptoms: Fall, Summer and Spring.

Fall allergies

Starting in late summer and throughout the fall, ragweed is the big seasonal allergy offender. Just one plant can produce up to 1 billion pollen grains, which are so light they can be carried on the wind for hundreds of miles.

In most parts of the U.S., ragweed season peaks in mid-September, but symptoms can last until the first frost of the year – so, it’s possible to have seasonal allergies in November.

Mold and dust mites can also trigger fall allergies – particularly when you need to flip on your home’s furnace for the first time. Raking up wet, fallen leaves can also stir up pollen and mold into the air, irritating allergies.

Spring allergies

Depending on where you live, spring allergy season can start as early as March and last through early summer. The release of tree pollens and outdoor mold spores are two of the most common spring allergy triggers.

Spring allergy symptoms include all the classics like sneezing, runny, itchy or stuffy nose, headache, itchy and watery eyes, and dry cough.

Summer allergies

During the summer months, pollens from grasses and weeds are to blame for allergy flare-ups. These summer allergies are in full swing by July.

Summer allergy symptoms are the same as spring allergy symptoms with runny or stuffy nose, sneezing, and itchy eyes, nose and throat.

Another big factor in the summer months can be pollution. While pollution is a concern year-round, the heat of the summer can have a big impact on air quality.