Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?

David Skoog credits COVID-19 with making him allergic to his own car. 

The 2013 Chevy Sonic used to serve as his respite from cramped New York subways. Now—four months after contracting COVID-19—Skoog is struck with an onslaught of symptoms every time he steps inside it. His lungs react first, with fits of wheezing and coughing, while his skin erupts in itchy red hives all over his limbs.

“There is an unknown airborne perfume or substance in my car that causes immediate respiratory distress,” Skoog tells Verywell. “The allergy literally came out of nowhere. I think it is tied to my altered sense of smell; I didn't lose it, but it became hyper-sensitive. Scents such as soap trigger a coughing fit.”

Skoog is a long-hauler, which means that while a viral test will declare him free from COVID-19, his body says otherwise. He suffers from a stream of debilitating symptoms such as fatigue, shortness of breath, brain fog, joint pain, and insomnia. They all combine to create what Skoog describes as “an everyday battle controlled by COVID-19.”

Fragrance allergies mark just the latest symptom COVID-19 long-haulers report experiencing, as experts try to pinpoint why.

Fragrance Allergies Are Pervasive

Most of the existing literature on COVID-19 and allergies focuses on how to distinguish between the two, as they can both manifest with similar symptoms:

• Shortness of breath
• Wheezing
• Headaches
• Sore throats

The notion that COVID-19 can concoct new allergies in patients is something that exists mainly in online support groups, specialists’ offices, and case reports like Skoog’s. Even more confounding is the substances that can trigger these allergies: a signature perfume, a soothing holiday candle, or even a Chevy Sonic.

However, fragrance allergies are not strictly a post-COVID-19 phenomenon.

Research shows that one in three adults experiences health problems after fragrance exposure. One study found that 30.5% of Americans are irritated by scented products.

Despite their prevalence in the population, fragrance allergies are still poorly understood. No proper diagnostic test exists. There are mixed views on whether it’s fragrances themselves that cause these allergies, or the chemicals that comprise them. Experts even disagree on whether these are allergies, sensitivities, or irritations.

What experts do know: Many of the mechanisms that trigger "traditional" allergies also underscore fragrance allergies. 

“If you have wheezing in response to fragrances, it’s likely that the fragrance is irritating and triggering the immune system which then produces chemicals to clear—what is being perceived as—an offense," Azza Gadir, PhD, an immunologist based in Los Angeles, California, and the director of research and development at Seed Health, tells Verywell. "This activation of the immune system results in inflammation and symptoms such as a runny, stuffy nose, watery, itchy eyes, wheezing, and hives."

For Skoog, the slightest scents set off his symptoms, even if they come from products that claim not to carry any fragrant notes, such as unscented soap.

“My allergies are, to some extent, quite terrifying,” he says. “I know it is something that is airborne and not contact-related. Since it is so unknown, I have no idea when I might come across something that triggers it and what might happen when that happens.” 

Skoog says his allergies are only amplified by his heightened sense of smell, a condition medically known as hyperosmia. He can now smell things from farther distances and can even detect the notes of a shower gel someone has used the day before.

How COVID-19 Could Trigger Fragrance Allergies

Gadir believes there could be multiple explanations for this COVID-19-induced allergic development.

“Everyone’s immune system is different, and these reports are rare, but it’s unsurprising that COVID-19 long-haulers are reporting sudden-onset allergies,” she says.

Gadir says the leading hypothesis for long-term COVID-19, like Skoog’s, is that patients’ immune systems remain activated or continue to overreact, despite clearing the virus. She says this hyperactivity can be modulated by regulatory T cells, which normally suppress the immune system and prevent inflammatory overreactions.

“When these cells don’t work, you can get allergies, which are inflammatory responses to otherwise benign agents, such as environmental allergens (fragrances) or foods,” she says. “We are still trying to understand the role that regulatory T cells play in COVID-19—establishing this will help us understand the nature of these allergies.”

She also emphasizes the effect mast cells—immune system cells found in connective tissue—have on this process.

“Mast cells play a key role in allergies, releasing potent chemicals like histamines and contributing to chronic airway inflammation,” she says. “Mast cells have also been shown to drive airway inflammation in COVID-19, and long-haulers can develop a disease very similar to Mast Cell Activation Syndrome (MCAS)."

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How Does Mast Cell Activation Syndrome Factor In?

Mast Cell Activation Syndrome is a chronic, multisystem disorder that can lead to allergic and inflammatory symptoms, as well as other symptoms like GI problems and neurological issues. As the name suggests, it's spurred by the hyperactivity of mast cells.

According to a report published this month, most of the hyper-inflammation witnessed in COVID-19 mimics the hyper-inflammation associated with MCAS. After comparing COVID-19 patients with and without MCAS, researchers concluded that the dysfunctional mast cells behind MCAS are also at the root of severe and long-term COVID-19.

This theory could possibly explain post-COVID-19 symptoms such as Skoog’s, as two common symptoms of MCAS are allergic reactions to fragrances and hyperosmia. 

Dustin Portela, DO, a dermatologist based in Boise, Idaho, has come across patients in his practice who present with hives connected to COVID-19. He also says that mast cells are involved in this symptom manifestation.

“Any time that we have urticaria (hives), there is usually a mast cell activation problem occurring,” he tells Verywell. “Here, mast cells will spill all their contents out and trigger blood vessels to dilate and fluid to leak out, which is why hives then appear on the skin.”

Gadir says that one way we can understand why mast cells, among other cell-types, are hyper-activated in COVID-19 is by studying regulatory T cells to see if they are unable to suppress mast cell hyper-activation.

“There are a lot of groups working on this right now, and I look forward to seeing their data and seeing which immunotherapies will be most effective for patients,” she says.

Can Other Viruses Trigger This Type of Allergy? 

While viral infections can induce wheezing illnesses and asthma, there are no documented viruses that trigger the same sudden-onset fragrance allergies sprouting from COVID-19.

“Viral infections such as respiratory syncytial virus (RSV) and parainfluenza virus cause wheezing and other airway symptoms,” Gadir says. “Viral infections (such as routine cold viruses) are also known to be the cause of more than 80% of all cases of acute hives in children.”

With regards to the hyperosmia associated with these fragrance allergies, most research on viral illnesses points to its direct opposite: anosmia. The fact that COVID-19 can steal a patient's sense of smell is a globally documented occurrence officially, now listed as one of the Centers for Disease Control and Prevention’s (CDC) COVID-19 symptoms. 

However, upper respiratory infections, many of which are viral in origin, can sometimes cause hyperosmia.

Treatment and Coping Options

In order to manage the epidermal effect of these allergies, Portela says mast cell functionality must be stabilized.

“Usually, we recommend medications like anti-histamines to do this. Benadryl is one of the most common anti-histamines in the U.S, but it often makes people drowsy,” he says. “Non-sedating antihistamines like Claritin, Allegra, or Zyrtec can also be effective, but they usually work better when you take them every day and don’t necessarily work quickly when you’re having an acute flare of hives.”

There are also certain respirators on the market that filter out fragrances and can help limit one’s exposure to a known allergen.

The main way to cope with fragrance allergies is to simply avoid triggers, which is something that Skoog says is difficult to do, as fragrances are found nearly everywhere.

However, as awareness about fragrance allergies spreads, many public spaces are now adopting fragrance-free policies. Airports such as Copenhagen and Helsinki are carving out designated fragrance-free routes for passengers, and some schools and hospitals are banning their employees from wearing perfume and cologne.

Skoog doesn’t know if his allergy to his car, as well as the rest of his debilitating symptoms, will ever go away. He says that the only constant thing that long-haulers know is that every day will bring a new surprise, and you never know whether it will be a good or bad one.

In the meantime, as fragrance-free initiatives continue to expand, they may offer Skoog and similar patients a small breath of fresh air—even if it only lasts a day.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.