Allergies in San Jose: Everything to Know

Written by Hannah Ward
Published: February 23, 2023
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Although San Jose has a longer-than-average allergy season due to its mild Californian weather, it has a reasonably low allergy ranking compared to many other U.S. cities. Despite this, many different plants can still trigger your seasonal allergies. In this article, we’ll discover when the peak times are for allergies in San Jose and which plants are the leading causes. We’ll also learn how your body reacts to pollen and why you have allergy symptoms. Plus, we’ll give you a few tips on how to ease your suffering during the allergy season.

When is Allergy Season in San Jose?

San Jose has an extended allergy season which begins in late January and ends in October or November every year. However, the peak months are April, May, and September. Despite this, San Jose ranks at only 97 out of 100 in the list of allergy capitals in the U.S. in 2022, as recorded by the Asthma and Allergy Foundation of America.

How Do Plants Cause Allergies?

Have you ever wondered just why your body is allergic to certain things? Well, the truth is it is down to misidentification. The body mistakenly identifies certain substances (such as pollen, pet hair, dander, food, and some drugs) as harmful. When this happens, an immune response is triggered in the body, and histamine is released. The body then attempts to drive the substance (the allergen) from the body. At this point, you experience some or all the symptoms of an allergy — a runny nose, watery eyes, sneezing, scratchy throat, itching, and congestion.

When it comes to plants, it is not the plant that triggers the allergy but the pollen it produces. Pollen is a fine, powdery substance. It comprises microscopic grains and comes from the male part of the plant. Pollen can be carried by birds and insects or carried by the wind. It’s when it comes into contact with our nose, mouth, and eyes that it can be a problem for allergy sufferers.

Plants that Cause Allergies in San Jose

Ragweed in bloom
Ragweed is the reason for the second allergy peak in San Jose in September.

© Carol Cenusa

Although we often talk about pollen as one substance, several different types exist. These include pollen produced by trees, weeds, or grasses. These typically pollinate at other times of the year. This is why the allergy season in San Jose has more than one peak in the year.


Trees typically pollinate during the spring. However, due to the mild weather, they can often begin to pollinate in late January. Maples, willows, and oaks are the main trees that cause allergies in San Jose. Maple trees, in particular, are known to be one of the leading causes of allergies in the U.S. They begin pollinating early, and their pollen can travel for many miles on the wind.


Although it may seem surprising, grass can produce significant amounts of pollen too. Grass typically pollinates during the summer months when the crops are all high. The grasses to avoid in San Jose are timothy, bent, rye, and Bermuda grass. However, ryegrass and Bermuda grass are the most allergenic.


Weeds have a habit of popping up where they’re not wanted; in this case, ragweed is the one you most want to avoid. Ragweed is the reason for the second peak in September. This is because it can produce millions of pollen grains from every plant. The other weeds to watch out for in San Jose are amaranth, sagebrush, saltbush, and smotherweed.

How to Treat Allergy Symptoms

Dog Park Series - San Jose Header
When the pollen count is high, there is a greater chance of you being affected by the pollen.


If you’re suffering from allergies in San Jose, then you’re probably wondering if there’s anything you can do to treat your symptoms, right? The bad news is that you’re unlikely to get them to go away completely. However, the good news is that there are a few things that you can do to make your life a little easier.

Avoid Your Triggers

We know this is easier said than done, but a few small changes can go a long way toward minimizing your exposure to the pollen that triggers your allergy symptoms.

  • Get an allergy test: An allergy test can help identify the substances you are allergic to. If you know exactly what you are allergic to, then it will be much easier for you to avoid them.
  • Check the pollen count: The pollen count measures the number of pollen grains in the air every day. When the pollen count is high, there is a greater chance of you being affected by the pollen.
  • Stay indoors: Although it is impractical to stay all the time indoors, it is advisable to stay indoors when the pollen count is particularly high.
  • Avoid gardening: Much like the point above, when there is more pollen in the air, your allergies will likely be triggered. Gardening jobs such as weeding, trimming bushes, and mowing the lawn can stir up allergens in the atmosphere. Therefore, it’s best if you can avoid these situations.
  • Keep your home clean: When there are allergens outside, the last thing you want is to bring them into your home. Keeping doors and windows closed, regular vacuuming, and using an air purifier or a HEPA filter is steps that can be taken. As pollen can stick to the fabric, you should also change your clothes after being outdoors for any time. Plus, don’t hang your laundry outside, or you’ll be bringing pollen indoors on your clean clothes as well.


Even if you’re unwilling to take medication, it can often be the most effective method of easing your allergy symptoms.

  • Antihistamines: Oral antihistamine tablets are one of the most common treatments for allergy symptoms. They block the effects of histamine — the substance in your body that reacts to the allergen. They can help with a runny nose, watery eyes, itching, and sneezing.
  • Corticosteroids: These are anti-inflammatory drugs in the form of a nasal spray. They are used to open the airways in the nose, which reduces the congestion caused by allergies.
  • Decongestants: These are often available as tablets or capsules and again work as a short-term treatment to relieve congestion.

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Calero reservoir
The deepest lake in San Jose is the Calero Reservoir, with a maximum depth of about 76 feet.
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About the Author

I have been writing professionally for several years with a focus on animals and wildlife. I love spending time in the outdoors and when not writing I can be found on the farm surrounded by horses, dogs, sheep, and pigs.

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