Can I Have an Allergy Without Knowing the Cause?

Yes, you can. Many people have allergies that are not diagnosed or are effectively hidden. Your allergic response can also be variable in degree. The diagnosis may be elusive as you may not respond the same way every time, or even to the same thing.

Key takeaways:
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    Hidden allergies can be both difficult to diagnose and treat.
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    Most commonly hidden allergies involve food, but they can include just about anything.
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    Hidden allergies can cause subtle symptoms and may pose particular challenges to both patients and clinicians.

Any diagnosis of any medical condition may be one of the most challenging aspects of medicine. So many of us rush to our own diagnosis based on a specific problem, usually highlighted by either a sign or symptom. This is known as a clinical diagnosis.

The reality is that making our diagnosis is often fraught with inaccuracies, as we don’t have enough information from medical tests or diagnostic procedures, and we don’t have experience in seeing other people with a similar clinical presentation. This is why patients come into the clinic or emergency room wanting a test such as a CT scan because then they feel more empowered to make their diagnosis or verify their suspicions with the doctor.

Of course, when we relent and go see a healthcare provider, it is usually because our remedies don’t seem to be working or we are getting worse. A major part is for the doctor to determine an accurate clinical diagnosis, not us. Surely, we think, if the doctor can make a diagnosis, then we are on our way to getting better since he or she will know what to do.

Unfortunately, clinical diagnosis can be tricky. Many signs and symptoms are nonspecific and overlap with other potential diagnoses. If the signs and symptoms are straightforward, then the diagnosis is called pathognomonic. If they are not, then the doctor creates a list of possible diagnoses or differential diagnoses.

Allergies can range from being an obvious (pathognomonic) diagnosis to difficult, overlapping with other diagnoses. Allergies can be hidden altogether, making them mysterious and frustrating to the patient, the patient’s family, and to the doctor.

Some patients may go on for years not really knowing what they are allergic to. Or they can be surprised by becoming allergic to something new that they had no idea was a potential issue.

What is an allergic reaction?

Our body’s immune system responds to foreign invaders for protection. When a foreign substance or antigen is detected, our bodies release antibodies to fight the invasion. Histamines and other substances are released to help our army of antibodies battle against the invader.

An allergic reaction is a hypersensitivity reaction. This is an exaggerated or overzealous response to the antigen. There are four types:

  • Type I reactions (IgE mediated): An example is anaphylaxis or a severe allergic reaction.
  • Type II reactions (IgG or IgM mediated): An example is drug-induced hemolytic anemia.
  • Type III reactions (immune-complex reactions): An example is serum sickness.
  • Type IV reactions (delayed hypersensitivity or cell-mediated immunity): Examples include poison ivy or nickel allergy.

Patients who are prone to Type I or IgE-mediated allergies are known as atopic. These are genetically disposed of hypersensitivity reactions.

Hidden allergies are usually atopic (Type I) or delayed hypersensitivity (Type IV) reactions. Many patients can have hidden allergies, particularly to different foods, and these are usually Type I or IV.

What makes an allergy hidden rather than a misdiagnosis?

Multiple portions of the immune system can cause a variety of hypersensitivity reactions. It is common for these hypersensitivity reactions to produce significant symptoms that mimic other disease states with similar signs and symptoms.

A useful and relevant example is having upper respiratory symptoms such as runny nose, sneezing, itchy eyes or throat, eye redness and watering, and nasal or chest congestion.

There may be a significant challenge in differentiating these symptoms from a simple cold, the flu, COVID-19, or allergies. There can be an overlap between a cold or flu and allergies. So, the cold may go away, but underneath is a hidden allergy that may cause symptoms to linger.

The most common hidden allergies

By far, the most common hidden allergies are in foods. It is so prevalent that it may affect as many as one-quarter of the population. With all the different ingredients being added to foods in preparation and for preservatives, it may be impossible to judge how big this problem is.

Some of the exposure to food allergies may be deliberate due to potential or deliberate contamination. Some food manufacturers are aware of these risks and place labels on some products to note that their products may be produced in machines that can be contaminated with nuts, for example. This warning is important for anyone allergic to nuts, as they may not be thinking about the food product containing nuts.

Other common hidden allergies may involve fish, eggs, or uncommon ingredients such as soy, mustard, or even honey. Not only is it difficult to determine what inadvertently was placed into the food, but it may also be equally difficult to figure out what the person is allergic to in food that seems okay to eat.

Food allergies can be especially difficult to diagnose. The person may experience skin symptoms such as a rash or hives, respiratory symptoms like wheezing or shortness of breath, nausea, vomiting, or even cardiovascular symptoms such as pale skin, weak pulse, dizziness, or even passing out.

Allergies can cause skin irritation and reactions, too. Some hidden allergies are related to perfumes, soaps, lotions, or even the base foundation in creating the product. A person is rarely allergic to a topical steroid, for example. But they can be allergic to different preparations of the same steroid product, making it extremely difficult to figure out the hidden allergy.

Where do potential allergens hide?

Here are some good examples. This is only a partial list of allergens containing peanuts, milk products, and fish and shellfish.


Chocolate/candy bars-barbecue sauces; Asian-style dipping sauces (particularly Szechuan); Curry sauces; Egg rolls, spring rolls; Trail mixes; Ice cream (peanut butter flavor or “Reese’s” ice cream); Certain body-care products and make-ups use peanut derivatives or peanut oil; Dog food or biscuits; Nonfood: bird seed, bird feeder, and traps.

Milk, dairy

Artificial butter, butter flavor, butter oil; Baked goods, e.g., cakes, cookies; Battered or fried foods; Broths and bouillons; Caramel coloring or flavoring; Chocolate, candies; Crackers; Coffee whiteners; Custards, puddings; Deli meats, hot dogs; Dips and salad dressings; Egg and fat substitutes (Opta, Simplesse); High-protein flour; Lactose-free products (don’t confuse with ‘dairy-free’; many contain milk protein); Malt drink mixes; Margarine (look for dairy-free brands); Sausages; Soy or rice cheese; Soups and soup mixes; Potatoes (instant, mashed and scalloped potatoes); Ghee (clarified butter) and butter fat; Kefir; Kumiss (fermented milk drink); Medications; Tuna fish (some canned brands).

Fish and shellfish

Ethnic foods: fried rice, paella, spring rolls, sushi (California rolls); Caponata (Sicilian relish); Gelatin, marshmallows; Pizza toppings; Salad dressings; Sauces, for example, marinara, steak, and Worcestershire; Spreads, for example, taramasalata (fish); Deli meats, hot dogs (from gelatin); Compost or fertilizers; Lip balm/gloss; Pet food; Deep fryers (used to cook fish, shrimp as well as other foods); Glucosamine and some calcium supplements (shellfish); Omega-3 supplements.

Allergy testing and hidden allergies

Standard allergy testing can include skin prick or scratch testing, intradermal testing, patch testing, or recent blood or IgE testing.

Many hidden allergies must be determined by challenge testing. This is akin to trial and error when it comes to food allergies. It is also recommended that it be performed under the supervision of an allergy doctor so that if there is a problem such as anaphylaxis (severe reaction) it can be handled appropriately.

More subtle environmental or food allergies can truly be hidden. Their identification and potential treatment may take time to diagnose.


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Amy Saunders Amy Saunders
prefix 1 month ago
Oh, really? Okay, I appreciate that you said we could easily undergo blood tests to determine if we're allergic to some substances. My son hasn't stopped sneezing since this morning which makes me wonder if he got in touch with any sensitive stuff. It would be smart if he meets a doctor immediately to treat the condition.