Allergies and Brain Fog: How Allergies Can Make It Hard to Think Clearly

Seasonal allergies (sometimes called hay fever) can cause several different symptoms. Some are easy to notice, like a runny nose, itchy eyes, and sneezing. But others are less obvious, like a sore throat or headaches. 

Brain fog is another symptom you may not immediately connect to your seasonal allergies. Brain fog is a term that describes trouble thinking or remembering things. If you’ve noticed that your thinking is less clear during allergy season, here’s what you should know about allergies and brain fog. 

Can allergies make it hard to think?

Yes, some people find it harder to think clearly during allergy season. In studies, people with seasonal allergies reported brain fog symptoms including: 

• Slowed thinking

• Memory problems

• Difficulty paying attention

Researchers note that seasonal allergies can make it hard for both adults and children to learn, remember things, and complete tasks. 

In one study, researchers noted that children performed worse on standardized tests during times when pollen counts were higher. A small study also found that children with untreated allergies performed worse on learning tasks compared to children without allergies.

A similar study found that adults with active and untreated seasonal allergies had more trouble remembering new words and completing tasks than adults without allergies. Another research study found that some adults with allergies even had these same difficulties during their allergy off-season.

So, there’s a clear connection between allergies and brain fog, or trouble thinking and completing tasks. Experts even recommend checking for allergies in kids who have trouble with school performance.

What are the symptoms of brain fog?

Brain fog isn’t a medical term. It’s a popular term to describe trouble with thinking, processing, or memory. 

Some common ways people describe brain fog include:

• Forgetfulness

• Feeling spacey

• Confusion

• Trouble paying attention

• Trouble focusing

• Having a hard time thinking

• Taking longer to process information

• Trouble remembering information

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People with brain fog may have one or more of these symptoms.

Why do allergies cause brain fog?

It’s not clear why people with seasonal allergies experience brain fog. But there are several things that likely contribute.

1. Interrupted sleep

Seasonal allergies can cause a runny or stuffy nose. They can also cause headaches or facial pressure. These symptoms can impact how well people sleep.

Some experts think that lower quality sleep is one of the main reasons people get brain fog during allergy season. 

Poor sleep can impact how clearly you think.For example, poor sleep can lead to: 

• Shorter attention spans

• Trouble switching course or adapting to unexpected changes

• Poor judgment

Long term, poor sleep can impact your memory. 

2. Medication side effects

Some allergy medications can make people feel very sleepy. For example, Benadryl (diphenhydramine) and Vistaril (hydroxyzine) are common allergy medications that can cause drowsiness. 

But these medications can do more than make you tired. They can also make it harder to focus or think clearly.

That’s why experts recommend antihistamine medications that don’t cause drowsiness. Medications like loratadine (Claritin) and cetirizine (Zyrtec) can provide allergy relief without contributing to brain fog.

3. Histamine release

Histamine is a chemical your immune system releases in response to allergies.

Research suggests that histamine may impact thinking and cognitive function. It plays a role in many important body functions including: 

• Sleep-wake cycles

• Attention

• Learning

• Memory

It’s possible that rapid changes in histamine levels can make it harder to think or concentrate.

How can you get rid of brain fog from allergies?

There are several things you can do to treat brain fog from allergies.

1. Decrease your exposure

Lowering your exposure to allergens will help ease allergy symptoms, including brain fog. 

If your allergies are worse from August to November, they’re probably caused by pollen. You can decrease your pollen exposure by: 

• Avoiding going outside from 5AM to 10AM (when pollen levels are highest)

• Keep windows in your home and car closed

• Drying your clothes in a dryer instead of hanging them on the line

If your allergies are worst in the spring, the cause is likely tree pollen. Avoid planting trees like oak, walnut, hickory, elm, and catalpa in your yard. 

If your allergies are worst in early to mid-summer, grass pollen is the most likely cause. You can decrease your exposure to grass pollen by: 

• Having someone else mow your lawn

• Keeping grass cut short

• Using other ground cover, like moss, for your lawn

• Using an air purifier indoors

2. Try over-the-counter allergy medications

There are many effective over-the-counter (OTC) allergy medications that don’t cause drowsiness. Loratadine and cetirizine are examples of nonsedating antihistamine medicines. Steroid nasal sprays can also help relieve a runny nose, stuffy nose, and sinus congestion. 

3. Daily nasal rinses

Daily saline rinses can help reduce allergy symptoms. They work by rinsing pollen out of your nasal passages before they trigger a reaction. You can use a Neti pot to do a daily rinse. You can purchase ready-to-use saline solution or make your own with saline packs and distilled water. Don’t use regular tap water to make saline rinses. 

When should you seek medical care for brain fog from allergies?

Many allergy symptoms can be treated at home. But it’s time to seek medical care if you’ve tried OTC medications, lowered your exposure to allergens, and used saline rinses — and still don’t feel better. You may need prescription medications to treat your allergy symptoms. 

You should also seek medical care if your brain fog symptoms are getting in the way of your daily activities. Don’t wait to ask for help if brain fog is making it hard to work, drive, sleep, or care for loved ones. 

It’s also a good idea to seek care if you’re not sure what’s triggering your allergies. Allergy tests can help pinpoint what you’re allergic to so you can avoid your triggers.

Why trust our experts?

Written by:

Amy Walsh, MD, MDP

I have worked as an emergency physician for 15 years, including care at both rural hospitals and trauma centers. I am the former Global Emergency Medicine fellowship director at Health Partners.

Edited by:

Patricia Pinto-Garcia, MD, MPH

Patricia Pinto-Garcia, MD, MPH, is a medical editor at GoodRx. She is a licensed, board-certified pediatrician with more than a decade of experience in academic medicine.

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