Metabolic Health 14 MIN READ

Guide to Allergies: What causes And How it Affects Metabolic Health?

Allergies can be incredibly debilitating, ranging from severe reactions which can result in hospitalizations to mild reactions which can impair functions of our everyday lives. What’s more, they can also affect our metabolic health.

Written by Team Ultrahuman

Dec 06, 2021
allergies cover image

Allergies can be incredibly debilitating, ranging from severe reactions which can result in hospitalizations to mild reactions which can impair functions of our everyday lives. What’s more, they can also affect our metabolic health.

What is an Allergy?

Allergies occur when the body reacts to foreign substances in the environment, which typically do not elicit a reaction in most people.

Our immune system produces special fighters called antibodies. When an allergic reaction occurs, the immune system produces antibodies that identify a specific substance (called an allergen) as harmful, even if it isn’t.

These antibodies then attack these allergens and trigger an allergic reaction, resulting in the inflammation of the sinuses, airways, digestive system, skin, etc.

What are the Symptoms of Allergies?

According to the NHS, most allergy symptoms are mild, but severe anaphylaxis (an allergic reaction that spirals out of control within minutes, explained below) can occur occasionally.

Let’s take a look at some of the symptoms segregated according to severity.

Mild Allergy Reactions

The symptoms, which are typically local and don’t spread to other body parts, include:

  1. Sneezing, itching, runny or blocked nose, also known as allergic rhinitis (AR)
  2. Scratchy throat with cough
  3. Red, itchy and watery eyes, also known as allergic conjunctivitis (AC)
  4. Raised red skin rashes, also known as hives
  5. Itchy, dry skin
  6. Nausea or vomiting

Moderate Allergy Reactions

The symptoms typically involve the entire body and include the following:

  1. Widespread hives
  2. Chest congestion and difficulty breathing
  3. Swollen lips, tongue or face
  4. Vomiting, diarrhoea and tummy pain

Severe Allergy Reactions

These symptoms may lead to a medical emergency:

  1. Chest pain or tightness with difficulty in breathing
  2. Abdominal cramping with severe nausea and vomiting
  3. Heart palpitations
  4. Dizziness or vertigo


Anaphylaxis is a rare, severe and sudden allergic reaction that develops within minutes. Its symptoms may include any of the above as well as the following:

  1. Swelling of the throat and the mouth with difficulty in breathing
  2. Confusion or anxiety
  3. Loss of consciousness
  4. Sudden and severe drop in blood pressure
  5. Blue skin

What Causes of Allergies or Common Allergens?

Here are the 7 different types of allergies:

  1. Pests: Dust mites, pet dander (composed of tiny, microscopic, flecks of skin shed by cats, dogs, or other animals with fur/feathers.), cockroaches, etc.
  2. Drugs: Antibiotics and anti-inflammatory agents like penicillin, sulfa drugs, aspirin and ibuprofen.
  3. Foods: Milk, mushrooms, shellfish, wheat, tree nuts (walnuts, pecans, almonds and cashews), sesame, soy, peanuts, egg and crustaceans.
  4. Insects: Venom from the stings of bees, mosquitoes, wasps, ants, and ticks.
  5. Airborne: Mould spores and pollen from weeds, trees, and grass.
  6. Plants: Poison oak, Poison ivy and other poisonous plants and latex from rubber plants.
  7. Chemicals: Chemicals in personal-care products, cosmetics, synthetic latex and industrial and household chemicals.

What happens in the body when you have allergic?

Our body has specialized immune cells called mast cells, which store the body’s supply of histamine, heparin and other inflammatory mediators. Also docked on the mast cells are immunoglobulin E (IgE) antibodies that detect the allergens as soon as they come in contact with the body.

How do allergies affect the body in three phases?

Early-Phase Allergy Reaction

An early-phase reaction occurs within minutes. It can be localized, like in the case of nasal congestion, as in AR and/or pink eye, also called AC, acute asthma attack or hives, etc. Occasionally, it can be widespread and life-threatening, like anaphylaxis.

The allergens release small chains of proteins called peptides, which attach themselves to IgE antibodies. When peptides bind to the IgE still attached to the mast cells, histamine and other strong chemicals are released, which trigger an inflammatory response in the body and the allergy symptoms appear.

Late-Phase Allergy Reaction

A late-phase reaction takes more time to develop and peaks 6–9 hours after exposure to an allergen. It typically follows an early-phase reaction and may take a couple of days to resolve.

Besides IgE, the T helper type 2 (TH2) and other white blood cells can also detect the peptides released by allergens, and that’s thought to be the reason behind late-phase reactions. These cells also release immunity-related chemicals as mast cells do. Late-phase reactions may involve redness, pain, oedema, warmth on the skin, airway narrowing and increased mucus secretion.

Chronic Allergic Inflammation

Chronic allergic inflammation is persistent, and it gets triggered only when your body gets repeatedly exposed to allergens. Due to constant or repeated exposure, the immune cells in that part of the body not only increase in number but also undergo significant changes to be ready for the allergen assault.

Moreover, to adapt to the allergic environment, the cells and the tissues in the affected area change in structure, function and/or size.

Metabolism, Inflammation, and Allergies

Immune cells, like other cells of the body, need nutrients to perform their function. Our lifestyle choices affect the metabolism of the immune cells, which plays an instrumental role in their regulatory or inflammatory responses to allergens.

Moreover, they also impact the evolution of the immune cells and the severity of their response to allergens. It means our way of life can profoundly affect how our body responds to common allergens.

What is Metabolism?

Metabolism occurs in every cell in the body. It is a series of chemical processes in each cell transforming the calories we eat into fuel to keep us alive. These processes sustain life, everyday functioning and include breaking down food and drink to energy and building or repairing our bodies.

What is Inflammation?

Inflammation is part of the body’s defence mechanism to protect us from a foreign invader. It can be a thorn or a sting or infection-causing pathogens such as viruses, bacteria, etc.

Inflammation can be acute (short-lived) or chronic (long-lasting). Acute inflammation lasts for a few hours or days, whereas chronic inflammation can linger on for months or years after the initial exposure to the inflammation trigger.

What is Immunometabolism?

Immunometabolism can be defined as an interdisciplinary field derived from a combination of classical immunology and metabolism, employing experimental advancements and paradigms of both fields.

The metabolism in the immune cells plays a vital role in initiating and maintaining the body’s reaction to foreign invaders. The body’s ability to adapt the immune responses to common triggers results from metabolic changes in the immune cells. These changes may be short-lived and see an acute reaction to a foreign invader, or they can be long-term, resulting in the metabolic reprogramming of the immune cells.

The Role of Immune Metabolism in Allergies

Immune cell metabolism is crucial for maintaining stable tissue conditions in the human body, also known as tissue homeostasis. In other words, the metabolic activities in the immune cells are responsible for the stable conditions necessary for the proper functioning of that tissue.

Can allergies cause inflammation in your body?

When the body encounters allergens, the innate and adaptive immune systems kick into action and disturb this delicate balance by altering the energy needs of the immune cells. The activated immune cells use up nutrients like amino acids, fatty acids and glucose and undergo functional and structural changes to regulate the immune responses and perform their effector functions of removing the pathogens from the body.

This shows that the severity of allergic reactions and inflammation is closely related to the availability of nutrients. Excessive saturated fatty acids coupled with hyperglycemia can exacerbate inflammation, especially when the pre-activated immune cells of the underlying disease are already present.

On the other hand, omega-3 fatty acids have been seen to decrease allergic reactions, thus highlighting the role of metabolism and diet in allergic reactions. Though the role of metabolism as it relates to immune allergies is not fully understood yet, the evidence suggests that immunometabolism plays a pivotal role.

The cells work hard to maintain the balance between the antioxidants and free radicals produced during metabolism throughout these changes. At the same time, cells also perform autophagy to clean up the damaged cells and impact the genetic patterns of the new cells (leading to evolution and adaptation).

Metabolic Allergies

Our metabolic health affects the way the body responds to allergens. Metabolic health is described as having ideal blood sugar levels, triglycerides, high-density lipoprotein (HDL) cholesterol, blood pressure and waist circumference without using medications.

These conditions include increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels. The onset and continuity of an allergic reaction and its severity are affected by various metabolic factors in the body. People with healthy metabolism are able to easily fight off allergens, and their immunity also improves.

However, people with metabolic syndrome are more susceptible to severe and chronic allergic reactions. Metabolic syndrome refers to a group of conditions that simultaneously occur, elevating your risk of heart disease, stroke and type 2 diabetes.

Can Allergic Rhinitis(Stuffy nose) Affect Blood Sugar?

We know that hyperglycemia can increase inflammation and, hence, exacerbate allergy symptoms. However, a Korean study found that the occurrence of blood sugar was significantly lower in patients with AR. At the same time, people with blood sugar had a lower likelihood of AR, irrespective of their gender, age, comorbidity, BMI and menopause. This means that people with AR had a lower risk of developing blood sugar than people without AR and vice versa.

Allergies and Insulin Resistance

Insulin resistance (IR) is a part of the metabolic-syndrome cluster. When the body is suffering from chronic inflammation, it can lead to insulin resistance. A study of 3609 Danish men and women (aged 30–60 years) found a strong connection between the high risk of allergic asthma and IR. (13)

Another research study found a strong correlation between IR and the antigen leukocyte antibody test (ALCAT), a food intolerance test. The majority of people who test positive for the ALCAT test also have TCF7L2 gene mutation, which can help treat and prevent IR (14).

Do allergies increase with obesity & High BMI?

People with higher BMIs and obesity often experience metabolic syndrome due to high sugars and lipids. Their adipose tissue is highly active, and they have local or systemic subclinical inflammation, contributing to repeated and severe AR.

Studies have also found a direct relationship between obesity and AR and found that childhood wheezing and AR can increase the risk of obesity in adulthood. (15)

Dr Silverberg of Northwestern University found in a study that children with asthma and hay fever were 1 percent more likely to be obese and overweight.

Can allergy cause high bp?

An allergic reaction can increase the blood supply to the affected area because it recruits white blood cells to initiate the immune response. At the same time, it can constrict the blood vessels, including some that lead to major organs. (16)

Immune cells also release pro-inflammatory factors, a known cause of atherosclerosis, i.e. the narrowing of blood vessels leading to elevated blood pressure and heart risks. (17)

Can Stress Cause Allergies?

Although stress doesn’t cause an allergic reaction, both undeniably go hand in hand. Our body responds to unexpected internal and external changes in the form of stress, and all the organ systems adjust to those changes.

Whether the stress is internal or external, our body releases a series of chemicals, mainly cortisol, but also histamine (18), to prepare the body for unforeseen circumstances. Histamine, as discussed before, is an inflammatory mediator and one of the reasons why stress can worsen or prolong the allergic inflammation in the body, producing even more stress on the body.

Our body’s stress-response system involves the autonomic nervous system (ANS) and the hypothalamic-pituitary-adrenal (HPA) axis, closely related to metabolic health.

HPA Axis, ANS and Allergic Inflammation

In case of stress or perceived stress, the HPA axis stimulates the release of cortisol through the ANS, which keeps the body on high alert.

What is Cortisol?

xCortisol is a hormone considered to be the body’s warning system. It regulates blood pressure, increases blood sugar and dictates sleep-wake cycles as well as how our bodies use proteins, fats and carbohydrates.

The frequent high cortisol levels due to persistent allergies, and subsequent glucose spikes, make people more susceptible to metabolic syndrome. (19)

However, cortisol has a complex yet balanced relationship with allergic inflammation. Many studies support the regulatory role of cortisol in the expression of allergic disease and related inflammatory responses, such as the risk of asthma associated with low cortisol levels or the higher efficiency of steroids in the evening when cortisol levels are low. (20)

Can Allergies Affect the Autonomic Nervous System?

The ANS is responsible for maintaining the stability of our internal functions. It affects all the involuntary muscles, many endocrine and exocrine glands and the functions of most tissues and organ systems in the body.

A team in Brazil studied the available literature to identify the role of ANS in the increasing correlation between asthma and AR—around 38 percent of patients with AR had asthma, and 78 percent of asthmatics had AR. (21)

The literature review pointed to increased activity of the parasympathetic nervous system, or decreased sympathetic system activity, in cases of AR. With asthma, they found that the changes in the ANS were secondary to other diseases.

However, these changes were due to the allergic reaction and not responsible for the allergic disease in both cases.

Allergies and Brain Changes

Allergies like AR reduce the number of immune cells in the brain but increase the number of neurons. Most neural materials increase occurs in the memory centre of the brain, i.e., the hippocampus. However, this trend decreases as the person gets older.

On the other hand, the number of microglia, the brain’s immune cells, decreased in seasonal allergies but increased following a bacterial infection. Barbara Klein from the University of Salzburg, Austria, concluded that the effect of the immune response on the brain depends on the type of the immune reaction.

How to Manage Allergies?

It may seem impossible to prevent constant allergic flare-ups, but managing your allergies isn’t as hopeless as you might think. Here are a few ways to avoid frequent allergy attacks.

Know your Allergens

Managing allergies is impossible if you don’t know the triggers. Some allergens are evident; for example, a flare-up after visiting a relative with a cat is a dead giveaway that you’re allergic to pet dander. Similarly, if you suffer from hay fever every season, you’re probably allergic to pollen.

However, since there are so many allergens, you might not be able to find what you’re allergic to on your own. In that case, you might want to visit your GP or an allergist to take allergy tests and identify the cause.

Once you have more information about your triggers, you can avoid them and stay allergy-free.

Reduce Allergen Exposure

Now that you know your allergens, all you have to do is minimize their exposure to you. Here are a few tips to keep allergens away from you:

  1. Reduce pollen exposure by staying indoors on windy days or by wearing a mask. Delegate gardening to someone else or postpone it. Remove clothes and shower as soon as you come back from outside, and don’t hang your laundry outside.
  2. If you’re allergic to animal dander, depending on the severity of the allergic reaction, you can create a safe zone for yourself, for instance, in your bedroom. Don’t let your pet enter that zone and remove any existing carpeting.
  3. Dust-mite exposure can be reduced by investing in allergy-proof bedding protectors and installing a high-efficiency particulate air (HEPA) filter.
  4. Keep the house cool and dry.
  5. Try and reduce stress as it can increase the duration and severity of your symptoms.

OTC Preventative Treatments

There are over-the-counter (OTC) remedies to help prevent and stop symptoms from allergies. Here is a list of some options you can find at your local pharmacy. (It is important to consult your doctor before opting for OTC medication):

  1. Use a saline sinus rinse to clean the nose of any allergens.
  2. If you’re at risk for anaphylaxis, it is recommended to carry your epinephrine auto-injectors everywhere. (Consult your doctor and get a prescription before using auto-injectors).
  3. Use OTC antihistamines to relieve common allergy symptoms like runny nose, watery eyes, sneezing and itching, etc.
  4. Consider using oral decongestants for temporary nasal decongestion. However, avoid prolonged use since they can cause rebound congestion, thus worsening your symptoms.


Allergies can affect the daily function of our lives, and in some circumstances be incredibly harmful, like with cases that result in anaphylaxis. The metabolism of our immune cells impacts our immune system’s ability to respond to foreign allergens. This in turn can impact the body’s ability to maintain stable tissue conditions. Our nervous system and stress response are intimately connected with our bodies’ reaction to allergies, with the HPA axis being key to our bodies’ reaction to stress and cortisol’s complex relationship with allergic inflammation. The best way to live around allergies is to know your triggers and take the proper precautions to avoid a flare-up.

Disclaimer:The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns and before undertaking a new healthcare regimen including making any dietary or lifestyle changes.



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