You’re sniffling. You’re sneezing. You’re itching. Is it a cold? A rash? You’re too old for it to be an allergy, right? Wrong. Kids aren’t the only ones who develop new allergies. In fact, adult-onset ­allergies are more common than you think. 

A study published recently in JAMA Network Open found that among people who have food allergies, nearly half developed at least one of their allergies during adulthood. Researchers who study allergies are not certain what is to blame for this general trend of growing allergies in both kids and adults. Some have speculated that it could be related to changes in our habits, such as the overuse of hand sanitizers and ­antibiotics…as well as changes in our diets.

Adult-onset environmental allergies are more common as well, possibly because rising temperatures are leading to larger amounts of pollen in the air. Those pollen rates also are believed to be responsible for increasing rates of environmental allergies among children.

Here’s what you need to know about adult-onset food and environmental allergies…

Food Allergies

If you have a bad reaction to shellfish (hives, itching, breathing problems)—even if it has never happened to you before—odds are that you are allergic. In fact, the most common adult-onset food allergy is to shellfish. Other likely allergens: Seafood, tree nuts, soy and peanuts, among other foods. 

Potential symptoms: Food allergy sufferers typically experience itching and/or hives within minutes or up to an hour and a half to two hours after consuming the food. Sufferers also might experience coughing, difficulty breathing, abdominal pain, nausea, vomiting, light-headedness and/or swelling of the lips, face, throat and/or tongue. 

Some exceptions… 

Recently, an allergy to red meat including beef and pork has been ­reported—the allergy is to a carbohydrate called alpha-gal, which can enter the body from a Lone Star tick bite. When someone who has been bitten subsequently eats red meat, he/she can suffer an allergic reaction that is atypical because it occurs several hours after consuming the red meat. 

It’s also important to distinguish between an intolerance and an allergy. Symptoms such as cramps, gas, diarrhea and bloating that occur several hours after eating, without itchiness or hives, may suggest an intolerance or your body’s inability to digest that food, but you are not allergic to it. Unlike allergies, these digestive issues do not occur because your immune response has misidentified a molecule in the food as something harmful.

Example: Many adults who have consumed dairy products without any issues for their entire lives suddenly start to experience cramping or gas after drinking milk or eating ice cream. These people have not developed a dairy allergy—they have developed lactose intolerance. Their digestive systems no longer produce enough of the lactase enzyme needed to digest a sugar found in dairy foods.

If you experience mild tingling or itching in your lips, tongue and/or throat after consuming certain fruits and vegetables, you might have a condition known as oral allergy syndrome, a very mild form of food allergy that actually suggests that you have a pollen allergy (see below for more about pollen allergies). A protein in the fruit or vegetable is so similar to a protein in pollen that your body is misidentifying it. Causes of common oral allergies include apples, carrots, celery, corn, kiwis, lettuce, oranges, peaches, peppers and tomatoes. What to do…

If you have a reaction that includes difficulty breathing, seek immediate medical attention. Many people don’t realize that they can fall victim to allergies as adults and may try to convince themselves that it is something else, such as a stomach bug or flu. That can be a dangerous mistake. Call 911. A person having a serious allergic reaction needs epinephrine right away to ensure that his airways stay open.

After experiencing any allergic reaction, write down everything you had consumed in the 90 minutes before symptoms appeared, as well as any meats you ate in the five hours prior to symptoms. Do this even if it was a relatively mild reaction that did not require immediate medical attention. If possible, write down not just the names of the food products consumed, but a complete list of ingredients in those products. If appropriate, take digital photos of the ingredients lists on food packaging.

Schedule an appointment to see an allergist approximately one month after your allergic response. Bring your list of suspect foods and ingredients to this appointment. Why wait a month to see an allergist? The allergist likely will conduct tests to determine what you are allergic to, and the odds of inaccurate test results increase during the weeks following an allergic reaction. In the meantime, avoid foods that you suspect might be the cause of your reaction—­particularly the most likely culprits, such as shellfish and other seafood, nuts and soy. 

Note: An initial mild allergic reaction does not guarantee that future reactions also will be mild—your next response could include potentially fatal anaphylaxis, which can constrict airways and cause a rapid drop in blood pressure. Warning: Do not try to confirm whether you have the allergy by consuming suspect foods again. 

If you do have a food allergy, the allergist likely will recommend that you avoid the food and carry an EpiPen Auto-Injector, a device that can be used to self-inject epinephrine if you were to have a severe allergic reaction in the future. Continued follow-up with your allergist—and yearly blood work—will help confirm if your allergy is persisting or has gone away. 

Environmental Allergies

It’s no secret that pollen, dust mites, mold spores and pet dander can trigger environmental allergies. But many adults are taken off guard when they suddenly develop environmental allergies, also called seasonal allergies or nasal allergies, in the years following a move to a different part of the country. There might be higher pollen levels in this new place…or different types of pollen than they have been exposed to in the past. Many people are allergic to certain types of pollen but not others. Similarly, their new home might harbor more dust or animal dander. 

Potential symptoms: People who have environmental allergies often feel as though they have colds that they can’t seem to shake, complete with runny noses, watery eyes and sneezing. But allergy sufferers typically also ­experience an itchy feeling in the throat and, potentially, in the eyes, nose and/or skin as well. If the allergy is to pollen, there likely will be a seasonal predictability to the symptoms—these people might believe they “come down with colds” every spring or fall, for example. 

What to do: Adult-onset environmental allergies are far less likely than food allergies to be life-threatening, though they can be very uncomfortable. People who experience them rarely require emergency medical attention or an EpiPen. It sometimes is possible to control the symptoms of environmental allergies on one’s own with over-the-counter medications such as antihistamines or steroid nasal sprays, but speak with your doctor before using these. 

Important: If you know that your environmental allergies appear predictably at a certain time of year, start taking these medications approximately two weeks before then. If you wait until the full-blown season to start medications, your allergy symptoms may be harder to get under control. Resource: Pollen.com gives local allergy forecasts on its national allergy map.

If over-the-counter medications fail to provide relief, see an allergist. The allergist might be able to fine-tune your use of over-the-counter medications or prescribe allergy shots or oral allergy immunotherapy. An allergist also can perform skin tests or blood tests to determine precisely which allergens are causing your problems, and he could suggest other solutions. 

Example: Perhaps you are allergic to dust mites, not pollen. If so, your symptoms might be dramatically reduced if you use allergen-proof bedding or a mattress cover, wash it frequently in water heated to at least 130°F, dust your home frequently using a damp rag, remove carpeting and/or install a HEPA filter air purifier.