Sudden food allergy: Dr explains causes and remedies

Summary: Sudden food allergies and intolerances in adults are more common than many realise, often triggered by immune shifts, gut health changes, or environmental factors. Food allergies involve the immune system and can be serious, while intolerances typically cause digestive discomfort. Common triggers include shellfish, nuts, dairy, and additives. If you experience unexpected reactions, it’s important to consult a GP for testing, diagnosis, and guidance on managing symptoms safely.

Imagine this scenario: you’ve been eating strawberries your whole life without a problem. Then one day—BAM!—your lips swell up like you’ve gone ten rounds with a beehive. Or maybe your favourite post-pasta comfort nap is replaced by cramps and a bloated belly. You’re not alone. Adult-onset food allergies and intolerances are more common than most people think—and yes, they can come out of nowhere.   

If you’re wondering why your body suddenly seems to be rejecting your go-to snacks, we’re going to look into the possible reasons, what to watch for, and what you can do about it. 

First, What’s the difference between a food allergy and food intolerance?

It’s important to start with this distinction, because even though the terms are often used interchangeably, they’re not the same thing at all. 

• Food allergies are immune system reactions. Your body mistakenly identifies a food protein as a threat and launches an attack, releasing chemicals like histamine that can cause symptoms ranging from mild (like hives) to life-threatening (like anaphylaxis). 
• Food intolerances, on the other hand, are usually digestive system issues. You might be lacking the enzymes needed to break down certain foods, or your gut might just not like what you fed it. Symptoms can be annoying and uncomfortable—bloating, cramps, gas, or diarrhoea—but they’re not dangerous in the way true allergies can be. 

A helpful rule of thumb – if your symptoms include skin rashes, throat swelling, or breathing difficulty, it’s probably an allergy. If it’s mostly tummy trouble, think intolerance. 

Why am I having food allergies all of a sudden?

This is one of the most bewildering questions for many adults. We tend to think of food allergies as a childhood thing—something you either grow out of or manage from early on. But the truth is, adult-onset food allergies are on the rise, and researchers are still working to understand exactly why.  Here are some of the current theories: 

Immune system shifts:

Our immune systems aren’t static—they can change over time, especially in response to infections, illnesses, or stress. In some cases, these changes can trigger new sensitivities. 

Gut health:

The bacteria in your gut (your microbiome) plays a huge role in immune function. Certain medications, diet changes, or even stress can disrupt that balance and potentially trigger new intolerances or allergies. 

Environmental exposures:

Moving to a new region, encountering new pollens or moulds, or even getting stung by a tick (yes, some tick bites are linked to red meat allergies – known as Alpha-gal syndrome) can trigger immune responses that cross-react with foods. 

Genetics:

If allergies run in your family, your body may just be hitting its tipping point later in life.  It’s not always possible to pin down one clear reason, but you're definitely not imagining it—and you're not alone. 

Also read: Why do people develop allergies later in life?

Common types and corresponding causes of food intolerance

Here’s a quick snapshot of the usual suspects: 

For allergies:

• Shellfish (like shrimp, crab, lobster) 
• Tree nuts (walnuts, almonds, cashews) 
• Peanuts 
• Eggs 
• Wheat 
• Soy 
• Milk 

Shellfish and tree nuts are particularly notorious for adult-onset reactions. You could eat them your entire life and suddenly, your immune system decides they’re the enemy. 

For intolerances:

• Lactose: As we age, our bodies often produce less lactase, the enzyme needed to digest milk sugars. This results in the abdominal bloating and discomfort. 
• Gluten: While coeliac disease is an autoimmune condition, many people develop non-coeliac gluten sensitivity later in life. 
• Food additives: Sulfites in wine, MSG in takeout, or artificial sweeteners can sometimes trigger digestive distress or headaches. 

Also read: Does having allergies mean your immune system is weak?

How long does it take to have a food allergy reaction?

With allergies, symptoms can show up within minutes but sometimes take up to 2 hours after eating. Severe reactions—especially anaphylaxis—usually happen fast, which is why it’s so important to take them seriously.    Food intolerances, on the other hand, often develop more gradually. You might feel fine after eating but then get hit with cramps or bloating a few hours later, making the connection a little trickier to spot. 

What should I do if I have allergy symptoms all of a sudden?

If you’re experiencing allergy symptoms for the first time—especially anything involving swelling, breathing difficulty, or dizziness—don’t wait it out. Seek medical attention immediately. Even if it turns out to be something less serious, it’s better to be safe than sorry.  For milder symptoms, here’s a quick action plan: 

1. Stop eating the food immediately. 
2. Take an antihistamine (like Benadryl) for allergy symptoms if advised by a healthcare provider. 
3. Document what happened. Keep track of what you ate, when the symptoms started, and how severe they were. 
4. Book an appointment with your GP or an allergist. You’ll likely need some tests—skin prick tests, blood tests, or an elimination diet—to figure out what’s going on. 

Can you “flush” a food allergy from your system?

Unfortunately, no. Once an allergic reaction is underway, you can't simply flush it out with water or wait for it to pass like a bad hangover. That’s why prevention and preparedness are key. If you’re diagnosed with a food allergy, your doctor might prescribe an adrenaline auto-injector (such as an EpiPen) and advise you on strict avoidance.    With intolerances, it’s a bit more forgiving. If your symptoms are mild, they’ll usually subside within a day or two after avoiding the culprit. 

Lifestyle shifts for living with new food sensitivities

Adjusting your life around a new allergy or intolerance can feel overwhelming at first—but many people adapt quickly and well. Here are a few tips: 

• Read every label. Foods you wouldn’t expect can cause unwelcome symptoms. 
• Cook more at home. Not only is it safer, but it’s also a great way to learn more about your body and what makes it happy. 
• Communicate clearly. Let restaurants, friends, and family know about your restrictions. Most people are more understanding than you’d think. 
• Keep a “safe snacks” stash at work, in your bag, or in the car to avoid hangry accidents. 

When to call your GP?

Always reach out to your healthcare provider if: 

• You have recurring symptoms after eating, even if they seem minor. 
• You’re not sure what’s causing your reaction. 
• You’ve had a reaction involving breathing issues, fainting, or swelling. 
• Your symptoms aren’t improving with basic interventions. 

A good GP can guide you to an allergist, arrange for testing, and help you understand whether this is something temporary—or a new reality. 

How can telehealth help with sudden food allergies?

If you experience sudden food allergies, telehealth can provide fast, convenient care when you need it most. With online doctor consults available 24/7, you can quickly speak to a GP about your symptoms, get advice, and access treatment without leaving home. Telehealth appointments make it easy to receive instant scripts online for antihistamines or other medications if appropriate. If further care is needed, your doctor can issue online referrals to allergists and provide medical certificates in Australia for time off work or study. Manage unexpected allergies safely and easily with telehealth.

Where to get support

You don’t have to figure this out alone. Organisations like Allergy & Anaphylaxis Australia (allergyfacts.org.au) and Australasian Society of Clinical Immunology (allergy.org.au) offer reliable information, support communities, and practical resources to help you live safely and confidently with allergies or intolerances.   

It might feel like your body is suddenly working against you, but in reality, it’s trying to protect you—even if it's being a little overzealous. With the right knowledge, support, and a few lifestyle tweaks, you can absolutely reclaim your comfort and confidence around food.