Of all the nicknames I have for my cat Calvin—Fluffernutter, Chonk-a-Donk, Fuzzy Lumpkin, Jerky McJerkface—Bumpus Maximus may be the most apt. Every night, when I crawl into bed, Calvin hops onto my pillow, purrs, and bonks his head affectionately against mine. It’s adorable, and a little bit gross. Tiny tufts of fur jet into my nose; flecks of spittle smear onto my cheeks.
Just shy of a decade ago, cuddling a cat this aggressively would have left me in dire straits. From early childhood through my early 20s, I nursed a serious allergy that made it impossible for me to safely interact with most felines, much less adopt them. Just a few minutes of exposure was enough to make my eyes water and clog my nasal passages with snot. Within an hour, my throat would swell and my chest would erupt in crimson hives.
Then, sometime in the early 2010s, my misery came to an abrupt and baffling end. With no apparent interventions, my cat allergy disappeared. Stray whiffs of dander, sufficient to send my body into conniptions mere months before, couldn’t even compel my nose to twitch. My body just up and decided that the former bane of its existence was suddenly totally chill.
What I went through is, technically speaking, “completely weird,” says Kimberly Blumenthal, an allergist and immunologist at Massachusetts General Hospital. Some allergies do naturally fade with time, but short of allergy shots, which don’t always work, “we think of cat allergy as a permanent diagnosis,” Blumenthal told me. One solution that’s often proposed? “Get rid of your cat.”
My case is an anomaly, but its oddness is not. Although experts have a broad sense of how allergies play out in the body, far less is known about what causes them to come and go—an enigma that’s becoming more worrying as rates of allergy continue to climb. Nailing down how, when, and why these chronic conditions vanish could help researchers engineer those circumstances more often for allergy sufferers—in ways that are actually under our control, and not just by chance.
All allergies, at their core, are molecular screwups: an immune system mistakenly flagging a harmless substance as dangerous and attacking it. In the classic version, an allergen, be it a fleck of almond or grass or dog, evokes the ire of certain immune cells, prompting them to churn out an antibody called IgE. IgE drags the allergen like a hostage over to other defensive cells and molecules to rile them up too. A blaze of inflammation-promoting signals, including histamine, end up getting released, sparking bouts of itching, redness, and swelling. Blood vessels dilate; mucus floods out in gobs. At their most extreme, these reactions get so gnarly that they can kill.
Just about every step of this chain reaction is essential to produce a bona fide allergy—which means that intervening at any of several points can shut the cascade down. People whose bodies make less IgE over time can become less sensitive to allergens. The same seems to be true for those who start producing more of another antibody, called IgG4, that can counteract IgE. Some people also dispatch a molecule known as IL-10 that can tell immune cells to cool their heels even in the midst of IgE’s perpetual scream.
All this and more can eventually persuade a body to lose its phobia of an allergen, a phenomenon known as tolerance. But because there is not a single way in which allergy manifests, it stands to reason that there won’t be a single way in which it disappears. “We don’t fully understand how these things go away,” says Zachary Rubin, a pediatrician at Oak Brook Allergists, in Illinois.
[Read: What they aren’t telling you about hypoallergenic dogs]
Tolerance does display a few trends. Sometimes, it unfurls naturally as people get older, especially as they approach their 60s (though allergies can appear in old age as well). Other diagnoses can go poof amid the changes that unfold as children zip through the physiological and hormonal changes brought on by toddlerhood, adolescence, and the teen years. As many as 60 to 80 percent of milk, wheat, and egg allergies can peace out by puberty—a pattern that might also be related to the instability of the allergens involved. Certain snippets of milk and egg proteins, for instance, can unravel in the presence of heat or stomach acid, making the molecules “less allergenic,” and giving the body ample opportunity to reappraise them as benign, says Anna Nowak-Węgrzyn, a pediatric allergist and immunologist at NYU Langone Health. About 80 to 90 percent of penicillin allergies, too, disappear within 10 years of when they’re first detected, more if you count the ones that are improperly diagnosed, as Blumenthal has found.
Other allergies are more likely to be lifers without dedicated intervention—among them, issues with peanuts, tree nuts, shellfish, pollen, and pets. Part of the reason may be that some of these allergens are super tough to neutralize or purge. The main cat allergen, a protein called “Fel d 1” that’s found in feline saliva, urine, and gland secretions, can linger for six months after a cat vacates the premises. It can get airborne, and glom on to surfaces; it’s been found in schools and churches and buses and hospitals, “even in space,” Blumenthal told me.
[Read: The next weird way we’re changing cats]
For hangers-on like these, allergists can try to nudge the body toward tolerance through shots or mouth drops that introduce bits of an allergen over months or years, basically the immunological version of exposure therapy. In some cases, it works: Dosing people with Fel d 1 can at least improve a cat allergy, but it’s hardly a sure hit. Researchers haven’t even fully sussed out how allergy shots induce tolerance—just that “they work well for a lot of patients,” Rubin told me. The world of allergy research as a whole is something of a Wild West: Some people are truly, genuinely, hypersensitive to water touching their skin; others have gotten allergies because of organ transplants, apparently inheriting their donor’s sensitivity as amped-up immune cells hitched a ride.
Part of the trouble is that allergy can involve just about every nook and cranny of the immune system; to study its wax and wane, scientists have to repeatedly look at people’s blood, gut, or airway to figure out what sorts of cells and molecules are lurking about, all while tracking their symptoms and exposures, which doesn’t come easy or cheap. And fully disentangling the nuances of bygone allergies isn’t just about better understanding people who are the rule. It’s about delving into the exceptions to it too.
How frustratingly little we know about allergies is compounded by the fact that the world is becoming a more allergic place. A lot of the why remains murky, but researchers think that part of the problem can be traced to the perils of modern living: the wider use of antibiotics; the shifts in eating patterns; the squeaky-cleanness of so many contemporary childhoods, focused heavily on time indoors. About 50 million people in the U.S. alone experience allergies each year—some of them little more than a nuisance, others potentially deadly when triggered without immediate treatment. Allergies can diminish quality of life. They can limit the areas where people can safely rent an apartment, or the places where they can safely dine. They can hamper access to lifesaving treatments, leaving doctors scrambling to find alternative therapies that don’t harm more than they help.
But if allergies can rise this steeply with the times, maybe they can resolve rapidly too. New antibody-based treatments could help silence the body’s alarm sensors and quell IgE’s rampage. Some researchers are even looking into how fecal transplants that port the gut microbiome of tolerant people into allergy sufferers might help certain food sensitivities subside. Anne Liu, an allergist and immunologist at Stanford, is also hopeful that “the incidence of new food allergies will decline over the next 10 years,” as more advances come through. After years of advising parents against introducing their kids to sometimes-allergenic substances such as milk and peanuts too young, experts are now encouraging early exposures, in the hopes of teaching tolerance. And the more researchers learn about how allergies naturally abate, the better they might be able to safely replicate fade-outs.
One instructive example could come from cases quite opposite to mine: longtime pet owners who develop allergies to their animals after spending some time away from them. That’s what happened to Stefanie Mezigian, of Michigan. After spending her entire childhood with her cat, Thumper, Mezigian was dismayed to find herself sneezing and sniffling when she visited home the summer after her freshman year of college. Years later, Mezigian seems to have built a partial tolerance up again; she now has another cat, Jack, and plans to keep felines in her life for good—both for companionship and to wrangle her immune system’s woes. “If I go without cats, that seems to be when I develop problems,” she told me.
It’s a reasonable thought to have, Liu told me. People in Mezigian’s situation probably have the reactive IgE bopping around their body their entire life. But maybe during a fur-free stretch, the immune system, trying to be “parsimonious,” stops making molecules that rein in the allergy, she said. The immune system is nothing if not malleable, and a bit diva-esque: Set one thing off kilter, and an entire network of molecules and cells can revamp its approach to the world.
I may never know why my cat allergy ghosted me. Maybe I got infected by a virus that gently rewired my immune system; maybe my hormone levels went into flux. Maybe it was the stress, or joy, of graduating college and starting grad school; maybe my diet or microbiome changed in just the right way, at just the right time. Perhaps it’s pointless to guess. Allergy, like the rest of the immune system, is a hot, complicated mess—a common fixture of modern living that many of us take for granted, but that remains, in so many cases, a mystery. All I can do is hope my cat allergy stays gone, though there’s no telling if it will. “I have no idea,” Nowak-Węgrzyn told me. “I’m just happy for you. Go enjoy your cats.”