Hypersensitivity means that your body reacts in a disproportionate or inappropriate way to a substance that’s not usually harmful.
Some people use the words ‘hypersensitivity’ and ‘allergy’ interchangeably, but it’s more complex: there are different types of hypersensitivity, as we’ll see below.
Unlike allergies, food intolerances don’t involve an overreaction of the immune system – they’re not a type of hypersensitivity.
Instead, food intolerances are usually localised in the gut, and although they’re unpleasant, they aren’t life-threatening. Symptoms typically include abdominal pain, bloating, excess wind and changes in bowel habits, like diarrhoea and constipation.
In this article, we’ll look at different types of hypersensitivity reactions and the symptoms they can cause. We’ll also explore the role your gut might play, and whether supporting your gut health could make a difference.
Reaction types
There are four different types of hypersensitivity (allergic) reactions.
Antibodies are proteins that your immune system uses, and the four types of hypersensitivity reactions differ depending on the types of antibodies involved.
The four types of hypersensitivity reaction are:
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Type I (immediate hypersensitivity): This is also known as an immediate allergic reaction. The first time you encounter an allergen that your body perceives as a threat, like nuts, eggs or soy, you won't have symptoms. This is called the sensitization stage, during which your immune system will produce specific IgE antibodies to the allergen.
These IgE antibodies then enter your bloodstream and attach to other immune cells, called mast cells and basophils, so that they’re ready to react to that allergen if you encounter it again.
The next time these IgE-loaded cells encounter the allergen, they trigger a cascade of immune molecules, such as histamine, which cause allergy symptoms. -
Type II (antibody-dependent reactions): This rare type of hypersensitivity reaction involves the production of IgG and IgM antibodies.
In this case, it can take 2–24 hours for the reaction to develop. The antibodies bind to molecules on the surface of cells and can lead to cell damage and death.
Medications like penicillin are often responsible for this reaction. -
Type III (immune complex-mediated reactions): This type also involves IgG and IgM antibodies, but here they bind to proteins, forming larger immune complexes that build up in tissues – such as skin, joints and vessels – and cause damage.
This reaction can take weeks to develop. It can result from insect stings or bites, and from taking medications that contain proteins from other species, such as antivenom.
Type III reactions play a key role in autoimmune conditions, such as rheumatoid arthritis and lupus. -
Type IV (delayed hypersensitivity reactions): This is the second most common type of reaction, and it includes contact dermatitis. Instead of antibodies, it involves immune cells called T cells.
The reaction usually occurs 2–3 days after exposure to the triggering substance, which may be anything from fungi or parasites to poison ivy, latex or metals, such as nickel.
Other conditions
For the most part, when people talk about hypersensitivity, they usually mean allergies, including food and drug allergies. This is the most common type of hypersensitivity reaction.
But type I hypersensitivities include many other conditions that involve your immune system, including:
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asthma
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rhinitis, which involves irritation and inflammation inside the nose
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conjunctivitis, also known as red-eye or pink-eye
Below, we’ll focus a bit more on type I because it’s what people tend to think of when they hear ‘hypersensitivity.’
Symptoms
There’s a wide variety of symptoms you might experience as part of a hypersensitivity reaction.
The kinds of symptoms can depend on the allergen – the substance triggering the reaction.
Allergies can range from mild to severe. And symptoms of a reaction can affect the whole body or just the area that made contact with the allergen.
The symptoms of a hypersensitivity reaction can include:
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rashes
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itchiness
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stomach pain
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swelling
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red eyes
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flushed skin
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sneezing
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wheezing
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diarrhoea
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vomiting
Some people with pollen allergies experience oral allergy syndrome. The symptoms often come and go quickly. They’re generally limited to the mouth and throat, and they include itching, tingling and slight swelling.
Oral allergy syndrome occurs because many plant-based foods, like fruits and vegetables, have a similar protein structure to pollen, and the immune system doesn't recognise the difference.
Anaphylaxis is a life-threatening allergic reaction. If someone suddenly experiences any of the following symptoms, they should receive immediate medical help:
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swelling of the lips, mouth, throat or tongue
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rapid or difficult breathing
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confusion
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drowsiness, dizziness or fainting
Learn more about feeling sick after eating.
Can improving your gut health help with hypersensitivity?
Because the immune system plays a central role in hypersensitivity, you may be wondering whether the gut microbiome is involved.
After all, around 70–80% of your immune cells are located in your gut. And the microbes living in your gut communicate with these cells, which can then influence the immune cells throughout your body. This relationship is known as the gut-immune axis.
Some people have a ‘leaky’ gut, which means that the gut lining allows more things than usual to pass through it.
Research in humans and animals suggests that a leaky gut could be a factor in developing food allergies – and may also increase the likelihood that allergens enter your bloodstream.
Scientists are investigating whether things that support your gut health, such as prebiotics and probiotics, could help with food allergies.
At the moment, research on using prebiotics and probiotics to manage food allergies has returned mixed results. Still, as our understanding of the gut-immune axis evolves, researchers continue to explore microbiome-targeted therapies as possible solutions.
Less studied than the gut-immune axis is the gut-lung axis. This is the relationship between the microbes living in your gut and those living in your lungs. Some studies have observed an imbalance in gut bacteria alongside an increased risk of developing asthma.
Meanwhile, some initial evidence suggests that certain probiotics might improve eye and nasal symptoms for people with hay fever.
While these findings may suggest that improving your gut health could help with hypersensitivity reactions, it’s worth noting that this research is still in its early stages. We need more studies to determine whether and how supporting gut health could influence allergies.
With that said, having a healthy gut can significantly benefit other areas of health. And because there’s usually little risk to following a gut-friendly diet, it’s worth doing what you can to keep your gut happy and healthy.
Learn 17 tips for supporting your gut health.
Diagnosing hypersensitivity
A doctor will want to explore your medical history and learn which substances you may have come in contact with before they diagnose hypersensitivity.
They can use blood tests to measure levels of antibodies, such as IgE, and these levels can indicate whether your symptoms are likely due to a hypersensitivity reaction.
If the doctor suspects that a particular trigger is responsible, they may then conduct other tests. In some cases, they may expose you to a small amount of the substance to see if it produces a reaction.
These tests include:
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skin testing, such as skin prick testing and scratch testing, for suspected food and airborne allergies
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drug provocation testing
Managing hypersensitivity
The main way to manage hypersensitivity is to avoid the substance that causes the reaction.
This may be easier said than done. Luckily, when triggers are difficult to avoid, such as pollen or dust, certain medicines can help, including:
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antihistamines, which block the effects of the chemical behind many allergy symptoms
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decongestants, which help open up your nasal passages
Corticosteroid medications can also ease some type III and IV reactions.
If these approaches aren’t improving your symptoms, a form of treatment called immunotherapy (also known as desensitisation) could help.
This involves gradually exposing yourself to increasing amounts of the triggering substance, and it can involve injections, tablets or oral drops.
Learn what you can do to support your immune system.
Does hypersensitivity go away?
Hypersensitivity can go away in some cases. For example, cow's milk protein allergy is one of the most common food allergies in babies and young children. Most children grow out of it by the time they’re 5 years old.
However, in most cases, hypersensitivity doesn’t go away. But with careful management, it’s possible to keep reactions at bay and relieve any symptoms that do arise.
Summary
Hypersensitivity means that your body responds to a particular substance as though it’s harmful. This response results from the actions of certain antibodies or white blood cells.
Some examples of hypersensitivity include food allergies, hay fever, asthma and contact dermatitis.
The main way to manage hypersensitivity is to avoid the substance that triggers the reaction. When this proves difficult, several medicines can help ease symptoms.
Emerging research suggests that your gut health may play a role in hypersensitivity. Scientists are still investigating how supporting your gut (and its healthy bacteria) might help.
Still, many other benefits of having a healthy gut are well-established. So, if you’re worried about hypersensitivity, there’s likely no harm in supporting your gut health alongside any treatments your doctor might recommend.
To learn more about other gut health topics, visit Symprove’s Gut Hub.
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