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Allergy Season In California: Allergens By Season & Region + Symptoms & Treatment

Allergy Season In California: Allergens By Season & Region + Symptoms & Treatment

Medically Reviewed By:
Dr. Shuba Iyengar, MD, MPH
Dr. Shuba Iyengar, MD, MPH
After graduating from UC Berkeley, Shuba completed medical school at Duke University, earning her MPH in tandem at UNC. After a research fellowship at the NIH, Shuba completed her residency at Stanford, then fellowship in allergy-immunology at Boston Childrens/Harvard.

Shuba returned to the Bay Area to join Dr. Bocian at a large multi-speciality health system where she helped lead an allergy practice. She cofounded Allermi to make expert allergy care more accessible for all.
Written by:
Katelyn Johnson, B.S., M.B.A, CMA
Katelyn Johnson, B.S., M.B.A, CMA
Katelyn Johnson is a freelance writer, Certified Medical Assistant, and Nationally Registered EMT with 8+ years of clinical experience across multiple specialties. She has a Bachelor’s in Biology, Master’s in Healthcare Administration, and is currently obtaining a Bachelor’s in Nursing. Katelyn is an advocate for providing patient education in an approachable way through online resources.

Seasonal allergies plague millions of people each year, though the allergens in the environment, severity, and peak time of year vary from state to state. The most dominant environmental allergen across the United States is pollen though every state has its own unique collection of pollen-producing plants. 

Additionally, each individual person varies in their sensitivity to pollen and other environmental allergens. Some do not experience any reaction at all during high pollen counts, while others may be highly allergic to tree pollen but not grass pollen. 

If you don’t want to go through professional allergy testing, it is easy to see what you are sensitive to just by learning what pollen-producing plants are in your area and when their peak pollen production is. 

For allergy sufferers on the West Coast, we have gathered the key information you need to know about allergy season in California. 

Below you’ll find which seasons are the worst for pollen allergies in California and what pollens are common in each region of the state. We’ll also take a look at the symptoms to look out for and an overview of treatment options. 


California Allergy Seasons

Different times of year in California are worse for pollen allergies than others and it is important to know when to expect a flare-up in your symptoms. 

Spring Allergies

Spring, which is considered March, April, and May, in California brings on a ton of tree pollen plus a moderate amount of weed and grass pollen. Spring is the worst pollen season of them all, especially if you are sensitive to tree pollen, though anyone with even mild allergies will likely have symptoms.  


Summer Allergies

Summer allergies are not quite as bad for those allergic to trees, though weed pollen production ramps up during June, July, and August. Grass pollen counts are about the same as in spring during the summer months. Late summer isn’t as bad as June and July which helps provide some relief after suffering since March. 


Fall Allergies

Fall, which includes September, October, and November, is when pollen levels start to settle down in California. Fall allergies are mostly from weeds, though grass pollen is still moderate during this time. Those with significant fall allergies are often highly allergic to grass and weed pollen.


Winter Allergies

In the winter, from December through February, there are low pollen levels all around. Due to the climate change that happens every winter, very few plants release pollen during this time in California. Only people who are highly sensitive will still experience symptoms.  


Common California Allergens By Region

The general severity of allergies each season is similar for all regions of California, though allergen species are localized by region


Northern California

The main population center of Northern California is the San Francisco Bay area and all of the surrounding cities. 

In this region, Cedar, Cypress, Juniper, Birch, Mulberry, Pine, Oak, and Walnut trees are major contributors to pollen production for much of the year. 

Weeds like the Biennial Wormwood, Perennial Ragweed, Mat Amaranth, and Coyotebrush alongside grasses such as Bermuda, Common Timothy, and Perennial Rye Grass are additional widespread allergens throughout the primary pollen season from March to August. 

Towards the fall and winter, the number of significant allergens in this region decreases significantly with only a few prominent weed and grass varieties such as Ragweed and Curly Blue Grass along with Privet trees remaining a problem.


Central California

The Central California Valley includes cities like Sacramento, Fresno, and Redding. As you might expect, due to its geographical location, the significant allergens of the area are a combination of the North and South. 

Big Sagebrush and several varieties of Willow, Mulberry, Ash, Oak, Maples, Juniper, and Cypress produce much of the tree pollen with the highest concentrations occurring between March and August. 

During spring and summer weeds in this area are Saltbrush, Wormwoods, Quailbush, White and Coastal Sagebrush, and Silverscale, as well as Bermuda, Common Timothy, Curly Blue, and Rye grasses, are prominent pollen producers as well. 


Southern California

In the two hubs of Southern California, which are San Diego and Los Angeles, allergy sufferers should look out for Olive, Mulberry, Willow, Cypress, Oak, and Ash tree varieties. 

In terms of weeds, several species of Wormwoods, Ragweeds, and Amaranths, as well as Sagebrush and Coyotebrush are prominent most of the year. 

Grasses to watch out for include Bermuda, Common Timothy, Rye, Spreading Bent, and Curly Blue which are less prominent in the winter, but still a concern due to the warmer weather than in other regions. 


Allergy Symptoms

Allergic rhinitis, hay fever, and seasonal allergies are all terms that are used to describe the group of symptoms that occur in reaction to environmental allergens. 

The most common symptoms include itchy eyes and nose, watery eyes, runny nose, post-nasal drip, cough, nasal congestion, sneezing, and a cough. You may experience just one or two of these, though it is possible that you have all of them at times. 

The severity of symptoms depends on how much of an immune response your body has to the environmental allergens which are usually trees, weeds, and grasses as we went over above. However, many people are allergic to other things in their environment like mold spores and pet dander, too.  


Treating Seasonal Allergies

There are three general methods of attack to fight off allergy symptoms each with its own benefits and disadvantages. 



Medications for allergy symptoms are commonly either oral or topical. 

Oral allergy medications are the pills you swallow like Claritin, Allegra, or Zyrtec. Oral medications can be effective and are of course easy to take, but tend to cause side effects in a significant number of people. 

Topical medications for allergy symptoms, which are predominantly nasal sprays, are the gold standard for treatment. Unfortunately, many nasal sprays on the market only treat one or two symptoms, requiring you to use multiple nasal sprays each day. 

Luckily, there is now another option available that treats all of your allergy symptoms with just one nasal spray. Keep reading to learn more about Allermi!


Allergy Shots/Drops

Allergy shots or drops work by exposing your immune system to small amounts of the things you are allergic to slowly over an extended period of time. This is designed for your immune system to be able to develop a natural defense against your triggers. 

Allergy shots take a long time to begin to control symptoms and frequently make them worse in the meantime. 


Lifestyle Changes

The final way to treat allergic rhinitis, or seasonal allergies, is to make lifestyle changes. Things you can do at home include using an air purifier, avoiding being outdoors for extended periods of time during peak pollen season, and washing fabrics in your home often. 

Keep in mind that though lifestyle changes will help keep some symptoms at bay, for those who have more severe allergies, it is unlikely to be as successful. 


As a quick reference, below are the answers to the most frequently asked questions surrounding allergy season in California. 


When is Allergy Season in California?

Allergy season in California is from around February 1st to November 1st, though the severity fluctuates and is highly dependent on your region since California is such a large state. 


Which State's Worst For Allergies?

Pennsylvania is often referred to as the worst state for allergy sufferers due to its extremely high pollen counts, though much of the Northeastern and Southern Midwest United States have challenging allergy seasons. 


Is California a Bad State for Seasonal Allergies?

California is not a bad state for seasonal allergies. In fact, California is often regarded as one of the best states to live in for allergy sufferers. 


What are the Most Common Allergy Symptoms in California?

The most common allergy symptoms in California are a runny nose, nasal congestion, post-nasal drip, and frequent sneezing.


Get Custom Allergy Treatment at Home

Rather than suffer through a slew of over-the-counter treatments to try and control your allergy symptoms, get custom allergy treatment from the comfort of your home. 

Allermi is a personalized allergy treatment designed by experienced, board-certified allergists, backed by science, and available delivered to your door in California. See the difference Allermi can make and start your free 30-day trial today!