After a week-long hospital stay, 61-year-old Chef Michael Chiarello died last week of a severe allergic reaction called anaphylaxis. Neither his doctors nor his family know what caused the fatal reaction, according to a representative for Chiarello’s company Gruppo Chiarello. Even so, his death sheds light on how serious and unpredictable allergies of all kinds can be. 

People can be allergic to nearly anything, including pollen, dust, food, insect stings, animal dander, latex, mold and medications. For many, all it takes is a tiny crumb or speck of an allergen to spark a reaction that can quickly become life-threatening if not treated properly or efficiently. 

Anaphylactic reactions most commonly occur to foods, insect stings, medications and latex, according to the American Academy of Allergy Asthma and Immunology. 

Chiarello’s family was not aware of any allergies he might have had, the Gruppo Chiarello representative told USA TODAY, but he was home when the reaction occurred. It’s still unknown what he was doing at the time of his reaction. 

Allergy experts say that Chiarello’s death serves as a critical reminder that even mild reactions can turn fatal, food labels are awfully confusing and adults can develop new allergies.

Yes, you can develop allergies in adulthood

Although most allergies arise in childhood, millions of adults go on to develop one or multiple allergies, even to foods or substances that they have safely been exposed to hundreds of times before, said Dr. Rita Kachru, an allergist with UCLA Health in Santa Monica, California. 

At least 15% of people with food allergies are first diagnosed in adulthood, according to FARE — a phenomenon that some researchers deem “an important emerging health problem.” 

Allergies sometimes emerge in adulthood because it takes time for your immune system to develop antibodies called immunoglobulin E against a certain food or substance that it mistakenly labels as dangerous, Kachru said. These antibodies “fight” the food by releasing histamine and other chemicals that trigger allergic reaction symptoms such as an itchy throat, difficulty breathing or vomiting. 

More often, adults may experience a reaction to an allergen they outgrew during childhood but for various reasons, such as changes in their immune system or environment, the allergy comes back, Kachru said. 

The surprise factor for many adult-onset allergies increases risks for anaphylaxis because people may not have an EpiPen (an auto-injector that releases epinephrine into the body to reduce inflammation) on hand. 

When allergies turn fatal 

Even mild allergies can lead to anaphylaxis, which is impossible to predict, Kachru said, because a reaction is dependent on exposure dose, the state of your immune system and prior history of allergic reactions. 

“If all it took was one cashew to trigger an allergic reaction the first time, the next time it may only take half a cashew to mount a response, which could be more severe,” Kachru said, “because you have primed your immune system by exposing yourself to it more.”

Treatment with an EpiPen is crucial in these scenarios, Kachru said, which should begin within seconds of the start of a reaction: “Inflammation is like a snowball — once it starts, it’s really hard to control.”

If an allergic reaction symptom worsens over time, if you develop two or more mild symptoms or if you have one severe symptom (like your throat closes up), use an EpiPen and then go to the hospital, Kachru said. Anaphylaxis can sometimes recur up to four hours after appropriate treatment in what's called a biphasic reaction.

Otherwise, treat a mild symptom with an antihistamine like Benadryl and stay cool, as heat can trigger a greater histamine response.

Learn about nasal spray epinephrine:FDA passes on first nasal spray alternative to epinephrine autoinjectors

Remember, allergens can be found in unexpected places

Never assume a food or object is free of your allergen, experts say, as it can lurk in the most unexpected places. 

Fish and shellfish, for example, are sometimes dipped in milk to reduce their fishy odor, putting those with dairy allergies at risk. Cross-contact — when an allergen is accidentally transferred from one food to another — can also expose you to an allergen, despite signs indicating a food is safe for you to eat. 

Don't shy away from asking people, whether it's your doctor, restaurant staff, whoever cooked your dinner, for details about how they prepared a meal, if cross-contact may have occurred, or what tools they'll be using on or around you, experts say. Doing so will help protect you from exposure to your allergen.

And double check those food labels

Federal laws require that the nine most common allergens —  milk, egg, peanut, tree nuts, soy, wheat, fish, shellfish and sesame — must be labeled on packaged foods sold in the U.S.

However, nuances in these laws allow certain ingredients outside of these top nine allergens to stay under the radar, according to the nonprofit FARE (Food Allergy Research & Education). Some may not be listed on the label, but instead may be covered by vague terms such as “natural flavorings.” Milk, Kachru says, could be listed as casein or lactalbumin, which are the proteins that make up milk. 

There are also no laws requiring manufacturers to say whether a product may have come into contact with a specific allergen. 

This is why you have to read food labels every time you buy a product. When in doubt, call the manufacturer directly to better understand what products contain or may contain.