Everything you Need to Know About Allergies (part 1): Causes, Symptoms, Diagnosis, and Treatments

Spring is the time for sunshine, green grass, and blooming flowers. But for some people, it’s the beginning of itchy eyes, continuous sneezing, and breathing troubles.

You get a new puppy for your son, but he can’t spend much time playing with it as he ends up having a runny nose and watery eyes. 

Yes, we are talking about allergies and almost anything can trigger it. Pollens, weeds, flowers, plants, insect bites, peanuts, milk, latex, certain medications, and the list keeps going on and on.

About 40 percent of the world’s population suffers from allergies and the number is on the rise. In India, more than 25 percent of the population suffers from allergies (1).

So what are allergies? How are allergies caused? Can they be even prevented? Can they be cured? Read on to learn everything you need to know about allergies and overcoming them.

What is an Allergy?

Allergies are reactions caused by the immune system in response to substances that are not typically harmful to the body.

Any substance that causes an allergic reaction is called an allergen. Most commonly inhaled or consumed, these substances trigger your immune system. Common allergens that can be inhaled include dust, pollen, and pet dander. But literally, anything can trigger an allergic reaction.

The causes of allergic reactions are varied. Allergies are often caused by food or drugs taken, there may be environmental triggers or the allergy is caused by organisms such as fungus or even mosquitos.

Allergens are of three primary types:

  • Inhaled allergens 
  • Ingested allergens
  • Contact allergens

Depending upon your body’s reaction, allergies can be mild, moderate, and even severe.

What are Allergic Reactions?

When an allergic individual is exposed to a particular allergen, it triggers an antibody response. This happens when you touch, inhale or swallow an allergen (2).

The antibodies produced attach themselves to the mast cells which respond by releasing histamine. This results in inflammatory symptoms such as rashes, itching, and sneezing.

Generally associated with increased immune responses to common allergens, atopy or atopic indicates a genetic tendency towards developing allergic diseases like eczema, allergic rhinitis, or asthma.

Allergic reactions may be limited to a specific body region or they may involve many parts of the body at the same time.

Types of Allergies

There are many types of allergies. Some are seasonal while others are year-round. Some can also be life-long.

British immunologists, Coombs and Gell have classified allergic reactions into four types. They are Type I, II, III, and IV. The first three allergic reactions are called ‘immediate types of allergic reactions’ as they occur within 24 hours of exposure to the allergen (3).

Type IV occurs after 24 hours of exposure and is known as delayed allergic reactions.

Type I hypersensitivity (immediate hypersensitivity) 

This type of allergic reaction involves the immunoglobulin E (IgE) mediated release of antibodies produced by the immune system. These IgE antibodies bind to the receptors present on the surface of the mast cell in the tissues and blood basophils, which contain histamine granules. They are released in the reaction and cause inflammation (4), (5).

The common allergens responsible for this kind of allergic reaction are pollen, animal dander, dust mites, and certain foods.

Type I hypersensitivity reactions are seen in allergic rhinitis, bronchial asthma, allergic conjunctivitis, allergic rhinitis, food allergy. Type-I hypersensitivity can even lead to anaphylactic shock (potentially life-threatening allergic reaction).

Type II or cytotoxic-mediated reactions

This type of allergic reaction is also known as cytotoxic reaction and is mediated by IgG and IgM antibodies. They activate the complement system that leads to cell damage or phagocytosis (6).

Type-II allergic reactions can be seen in conditions like autoimmune hemolytic anemia, immune thrombocytopenia, and autoimmune neutropenia. Good pasture syndrome, Pemphigus, are also examples of Type II hypersensitivity.

Type III or immunocomplex reactions

Also known as immune complex reactions, Type III allergic reactions involve IgG, IgM, and sometimes IgA antibodies. These antibodies react with the soluble allergens and build up immune complexes (antigen-antibody complexes).

The complement system activation that takes place, as a result, releases chemotactic agents (substances that stimulate cell migration), thereby attracting neutrophils and causing inflammation and tissue damage.

These types of reactions can be seen in lupus, serum sickness, and Arthus reaction.

Type IV or cell-mediated reactions

Popularly known as delayed-type, TYpe-IV reactions involve T-cell mediated reactions. These T-cells or macrophages are activated as a result of cytokine release, leading to tissue damage.

Many long-term diseases such as tuberculosis and fungal infections are examples of these reactions. Certain skin allergies especially to metals are also Type IV reactions.

Causes of Allergies

As mentioned earlier, allergy causes can be anything from airborne allergens, foods, insect stings, and medications to latex, metal, cosmetics, or even pets (7).

Food Allergies

Food allergies are common but less common than food intolerances. Food allergy occurs when your immune system reacts abnormally to certain foods you eat. They are often a result of the immune system wrongly recognizing some of the proteins in foods as being harmful (8).

Most food allergies have symptoms like hives, wheezing, and stomach pain. Studies show that 8 different types of food cause about 90 percent of all food allergy reactions. They are:

  • Cow’s Milk
  • Egg
  • Peanut
  • Tree nut which includes brazil nuts, almonds, cashews, macadamia nuts, pistachios, pine nuts, and walnuts
  • Soy
  • Wheat
  • Fish
  • Shellfish (crustaceans) which includes shrimp, prawns, crayfish, lobster, squids, and scallops

But food allergies do not limit themselves here. There is a big list that can trigger allergic reactions. You may have many questions regarding the causes of allergic reactions. Can coffee cause allergies? Can wine cause allergies?

Yes, they can. According to a 2012 study published in the International Archives of Allergy and Immunology, green coffee bean dust caused allergic reactions in some who worked in the coffee processing industry (9). Wine contains grapes, ethanol, and yeast, any of which can act as an allergen. Ingredients used for fining the wine can also be the cause (10).

And the list goes on. Some more foods that tend to cause allergic reactions are black pepper, sesame seeds, banana, avocado, mustard seeds, aniseed, chamomile, seafood, sunflower, lemon, GMO, MSG, mint, pea protein, and nightshades.

Environmental Allergies

Environmental changes such as global warming are thought to be the main factor in the increasing number of allergic diseases (11).

Seasonal Allergies

As the seasons’ change, from winter to spring and summer, each brings its share of allergens.

Spring allergies: Spring allergy is mostly triggered by pollen. For some, their immune system mistakenly sees the pollen as a danger and releases antibodies that cause reactions. Triggers include pollen from trees such as alder, ash, aspen, beech, box elder, cedar, hickory, cottonwood, juniper, oak, olive, and palm. The grasses and weeds that cause spring allergies are Bermuda, Fescue, Johnson, June, redtop, sweet vernal, and timothy.

Summer allergies: These allergies are usually triggered by pollen from grasses and weeds. The real culprits are ryegrass and timothy grass. In fact, the Asthma and Allergy Foundation of America states that grasses are the most common triggers of hay fever (12).

Fall allergies: Ragweed, mold, and dust mites are the main culprits triggering fall allergies. Other ones are nettles, mugworts, sorrels, fat hens, and plantains.

Winter allergies: Winter allergies are mostly related to mold, pet dander, cockroaches, and dust mites. As you spend time indoors, the allergens that lie dormant can trigger allergic reactions.

Rain allergies: Can rain cause allergies? Oh, yes! Rain brings with it its share of allergic reactions. When the grass and weed pollen is high, raindrops that hit the ground break the clump of pollen into smaller particles. This then quickly disperse in the air and cause allergic asthma symptoms (13).

Allergic Environmental Substances

Cotton: Textile allergy is extremely rare. Cotton clothing may cause skin irritation but cotton allergy is related to the exposure of cotton dust in the air that could lead to airway obstruction. Molds such as Alternaria and Aspergillus that are occasionally found in cotton crops can be the cause. Other natural contaminants of cotton are bacteria and endotoxins can trigger allergic reactions (14).

Tobacco Smoke: Can smoke cause allergy? Many people feel that they are allergic to smoke from tobacco especially cigarettes, cigars, or pipes. The common symptoms that they experience are mainly breathing trouble, wheezing, watery eyes, headaches, runny nose. However, most doctors believe these allergic-like symptoms aren’t actually smoke allergies. The chemicals and toxic ingredients in tobacco products trigger a reaction in people who are sensitive to those specific substances (15).

However, there has been an incidence of contact dermatitis on touching tobacco products. Some have also reported allergic reactions in the mouth and lips while chewing tobacco.

Respiratory Allergies

Respiratory allergies, also known as allergic rhinitis (AR) are caused by the proteins in the air that when inhaled trigger inflammation of the airways. Specific allergens such as smoke and fumes can aggravate these reactions. It induces IgE-mediated response and shares many symptoms with allergic asthma (16).

Respiratory allergies can be caused by various components such as pollen, dust mites, pets, mold, etc. Sometimes allergy symptoms are seasonal. A warmer climate leads to longer pollen seasons as an effect of climate change. Therefore an increased risk of respiratory allergic reactions is taking place.

Respiratory allergies can develop from mites, animal skin, fur, and mold.

Allergies Caused by Chemical Agents

Allergies from chemical agents are quite common. This includes artificial flavoring, preservatives, and antibacterials added to food products to increase their shelf life. Chemical substances used to thicken or lubricate a product can also very well be the cause.

Chemicals in hair dyes and different hair products can also be potential allergen. Other than that, formaldehyde resin, an ingredient in nail care products and chemicals in lip balms, sunscreen, and moisturizer can also lead to allergies.

  • Sulfite allergy: Some food, drinks, and medications contain sulfite as a preservative that can cause allergic reactions. Some people also react to medications that contain sulfonamide such as certain antibiotics. This is different from sulfite allergy though (17).
  • Sulfur dioxide: Sulphide dioxide is a natural component that is produced while making beer and wine. It is also often used in the wine. People who are asthmatic or are prone to allergic rhinitis may react when inhaled sulfur dioxide. Some people have experienced asthmatic attacks after drinking acidic drinks that contain sulfites.
  • Latex allergies: Latex allergies often occur while using latex gloves and condoms.
  • Perfume or Fragrance Allergy: Perfume allergy or fragrance allergy occurs when you have an allergic reaction after being exposed to them. It can result from getting sprayed, touching the liquid, or inhaling it. Several surveys reported that about 30 percent of the population of the United States complain of irritation from perfume (18).

More than 2500 fragrances are used in cosmetics that can cause fragrance allergies and are often unlisted. Fragrances in soaps, colognes, deodorants, moisturizers, cosmetics, and detergents can trigger an allergic reaction.

Metal Allergies

Metal allergies especially nickel, zinc, chromium, titanium, sterling silver, stainless steel, cobalt, silicon, and gold. In metal allergies, the skin cells pick up small molecules of metal that travel to the lymph nodes. Those substances are considered foreign invaders and trigger an immune response (19).

Plant and Pollen Allergies

Plant allergies are caused by pollen and resin. Pollens from weeds, trees, and grass and resin from plants like poison ivy and poison oak are very common plant allergens (20).

  • Pollen Allergy: Pollen allergy, also known as hay fever is often referred to by the experts as seasonal allergic rhinitis. During spring, summer, and fall, plants release pollen grains that trigger allergic reactions. Some people have pollen allergies all year round whilst others have them only during specific times of the year.

People who are sensitive to birch pollen suffer during spring while those with ragweed allergies are affected during late spring and early fall.

Drug Allergies

A drug allergy is caused because of an abnormal reaction of your immune system to a medication. Drug allergy is a type of unpredictable reaction that refers to immunologically mediated drug hypersensitivity reactions (21).

Drug allergies are normally IgE or non-IgE mediated. Adverse drug reactions (ADRs) account for 3-6% of all hospital admissions and occur in approximately 10-15% of hospitalized patients.

Sulfa allergy is a drug allergy often reported and is associated with sulfa drugs. These drugs are mainly used to treat a range of health problems. Such as rheumatoid arthritis and eye infections.

Sulfa drugs, also known as sulfonamides, are used to treat many infectious diseases and are found in antibiotics and other drugs. Sulfamide allergy can be the cause of antibiotic allergies.

Some other drug-related allergies are:

  • Penicillin allergy
  • Aspirin allergy
  • Clindamycin allergy
  • Iodine allergy
  • Steroid allergy
  • Other common drugs such as NSAIDs, amoxicillin, cephalosporins, local anesthetics, general anesthetics, and sulfa drugs can also be the cause of allergic reactions.

Allergies Caused by Hormones and Neurotransmitters

Hormonal allergy is an allergic reaction caused by one’s own hormones. This can interfere with the normal functioning of the hormones and can occur premenstrually in women along with the variation in the menstrual cycle (22).

  • Mast cells produce and store histamine, the chemical responsible for inflammatory reactions of allergies. These cells also have estrogen and progesterone receptors.

Therefore when estrogen binds to its receptors on these cells, it triggers histamine production and release. So the more is estrogen the more is the histamine release that leads to a vicious histamine-estrogen cycle. Estrogen also affects histamine metabolism by reducing DAO enzyme activity leading to more histamine production but less histamine excretion. This causes histamine intolerance and reaction.

Histamine intolerant women experience headaches and other symptoms at ovulation or right before periods.it can also cause more menstrual cramping.

  • Adrenal glands produce cortisol that plays a crucial role in controlling the body’s histamine levels. Therefore when this cortisol level is low that is during cortisol deficiency, can lead to allergic reactions. However, do keep in mind that stress doesn’t actually cause allergies but it can make allergic reactions worse by increasing histamine production in your bloodstream.

Allergies Caused by Organisms

Microorganisms such as fungus, yeast, virus, mold, and bacteria can lead to allergies. Bacteria, fungus, or viruses can also cause infectious rashes. Common viral rashes include mononucleosis, chickenpox, and shingles.

Other allergies caused by organisms are:

Mold allergy: Mold allergy is triggered when you breathe in mold spores. Mold and mildew are fungi. Their seeds are called spores which travel through the air. Some spores in foggy weather when the humidity is high. Others spread in dry, windy weather. Inhaling these spores can cause allergic reactions (23), (24).

Dust mite allergy: This is an allergic reaction that is triggered by tiny bugs that live in house dust. The symptoms of dust mite allergy are very much like hay fever. They are sneezing and runny noses. In some people, dust mite allergy can lead to wheezing and breathing difficulties including asthma (25).

Yeast allergy: Even though rare, IgE-mediated yeast allergy does exist. It can affect your whole body causing skin reactions, abdominal bloating, breathing difficulties, dizziness, and pain in the joint. Sources of yeast allergy maybe bread and baked goods, yeast-containing alcoholic beverages, aged meats and olives, mushrooms, and fermented products. Yeast allergy can be the cause of wine allergy and beer allergy (26).

Insect sting allergy: This can be caused by the stings of mainly five insects. They are honey bees, hornets, wasps, yellow jackets, and fire ants. Usually, insect stings cause non-allergic reactions that are concentrated to the bite area and result in local pain, itching, swelling, and redness. It lasts for 48 hours up to one week.

Insect sting allergic responses occur in people who have developed antibodies against insect venom from prior exposure. Around 0.3-3% of stings trigger this systemic allergic reaction.

Mosquito allergy: Mosquito allergy results from allergy to mosquito bites. It is also referred to as Skeeter syndrome. People with this syndrome are extremely sensitive to these bites and can develop allergic reactions such as fever (27).

Pet allergy: An abnormal immune reaction to proteins in an animal’s skin cells, saliva, or urine is termed as pet allergy. It is relatively common and often leads to sneezing, runny nose, wheezing, and/or difficulty breathing. Pet dander is tiny flecks of skin that are shed by pets such as cats, dogs, rodents, birds, and some other fur animals. Also known as pet dander allergy, these particles can cause allergic reactions in some (28).

Allergies from fish and reptiles are rare but present.

Development of Disease

To understand allergies better, you first need to know how are allergies caused.

1. Development of Food Allergies

Food allergies can be immunoglobulin E (IgE) mediated and non-IgE mediated. IgE-mediated allergic reactions are immediate whereas non-IgE mediated which take up to 48 hours or more to develop.

Systemic inflammation (SI): This kind of inflammation is a result of the release of pro-inflammatory cytokines from the immune-related cells and the chronic activation of the innate immune system. Some specific food antigens are shown to trigger this response resulting in Systemic inflammation leading to food allergy.

Leaky gut and food allergy:  Impaired gut barrier function leading to the leaky gut can result in food allergies and food intolerances. In a leaky gut, the increased intestinal permeability leads to the leaking of undigested food into the bloodstream. The body renders it as a possible threat or allergies triggering allergic reactions (29), (30). It can also trigger autoimmune diseases such as inflammatory bowel disease, celiac disease, autoimmune hepatitis, type 1 diabetes, and systemic lupus erythematosus (SLE).

Gut microbiome and food allergy: The trillions of microbes that live in us (our gut microbiota) help suppress immune responses to food by stimulating the TLR4 receptor. This TLR4 receptor sits in the membranes of the immune cells and helps recognize the microbes, if damaged can cause allergic reactions (31).

In our gut, the microbes that colonize there release more regulatory T-cells, a type of cell that negates or lowers immune responses. These act as a gut barrier. If your gut microbiome dwindles due to antibiotics or anything, it may break this delicate balance increasing the episode of food allergies. 

Tight junction and food allergy: The intestinal tract is considered to be a barrier to food allergens. Tight junctions play an important role in intestinal permeability maintenance which is considered to be the barrier that determines selective cellular absorption (32). Tight junctions consist of multiple proteins as a functional complex. Certain allergens can trigger a mechanism that jeopardizes tight junction permeability rendering intestinal barrier damage and consequently food allergy. Studies have shown that allergen-induced abnormal expression of proteins in tight junctions can also lead to inflammatory bowel disease, chylous diarrhea, and celiac disease.

2. Development of Respiratory Allergies

Lung microbiome and respiratory allergies: The microbiome is defined as the “ecological community of symbiotic and pathogenic organisms that share our body space” (33). These play a crucial role in maintaining organ, tissue, and immune homeostasis.  Any factor compromising this microbiota compromises this balance and weakening of the immune system and respiratory allergies (34).

Leaky gut and respiratory allergies: Leaky gut is also known as intestinal permeability. In this condition, the lining of the digestive tract becomes inflamed and porous thereby allowing undigested foods such as bacterias, yeasts, and certain other toxins to enter the bloodstream causing respiratory problems and allergies.

Asthma is one of the allergic diseases caused by intestinal permeability or leaky gut (35).

3. Development of Skin Allergies

Skin acts as a primary barrier to millions of external pathogens. Therefore this barrier function is of utmost importance for maintaining skin homeostasis. Any dysfunctionality can lead to enhanced penetration of these allergens and the development of skin allergic diseases such as atopic dermatitis. Skin allergies can be atopic dermatitis (eczema), allergic contact dermatitis, urticaria (hives), and angioedema.

Skin microbiome and cutaneous allergy: Our skin acts as a physical barrier that prevents the invasion of harmful bacteria (36), (37). Skin is home to millions of friendly microorganisms called the skin microbiome that keeps our skin healthy and in good condition. A disruption in the microbiome can create inflammation, irritation, dry and itchy skin, and cutaneous allergy such as urticaria, contact dermatitis, etc.

Leaky gut and skin allergy: We already know that leaky gut can lead to respiratory and food allergies. But now studies have concluded that leaky gut can also lead to skin allergies such as acne, atopic dermatitis, and psoriasis (38), (39), (40).

Downstream: The Long Term Consequences of Allergies

Allergies are much more than minor discomforts such as rashes, watery eyes, or redness. Allergic reactions can have serious, long-lasting effects if left untreated. They can become more than a seasonal or periodic nuisance and can greatly affect your quality of life.

Untreated allergies can have severe reactions related to the skin, ear, nasal passage, sinuses, and digestive system. Untreated allergies can cause secondary infection and can worsen other chronic problems such as asthma, eczema, and hives on the skin.

Some of the physical complications can be:

1. Respiratory

  • Bronchial asthma: It is a chronic inflammatory disease in which the airways become inflamed and swollen. This results in tightening of the muscles around the airways causing them to narrow down leading to difficulty in breathing (41).
  • Allergic rhinitis: Allergic rhinitis is caused because of the allergen in the air that enters your system and presents symptoms such as sneezing, nasal congestion, postnasal drip, and nasal pruritus. It is an Ig-E-mediated immune response (42).
  • Sinusitis: Sinusitis can be defined as the inflammation of your sinuses. These are small air pockets behind your forehead, nose, cheekbones, and the middle of the eyes. They produce mucus that protects the body from germs by trapping in the flowing liquid. Seasonal allergies cause acute sinusitis but persistent allergies can cause chronic sinusitis (43).
  • Allergic bronchitis: This is a chronic, respiratory allergic reaction that is triggered by tobacco smoke, dust, or pollution. 
  • Pharyngitis: The inflammation of the pharynx (in the back of the throat) is known as pharyngitis. It can cause sore throat, difficulty swallowing, sneezing, runny nose, chills, fevers, and cough (44).

2. Skin

  • Atopic dermatitis (AD)/Eczema: It is a chronic skin condition caused by allergic reactions. It causes itching and redness that turns into a red rash. Acute atopic dermatitis produces oozing plaques of very itchy skin and chronic atopic dermatitis manifests itself as thickened, elevated plaques (45).
  • Hives/ Urticaria: Hives are a common skin rash that is triggered by factors such as medication, insect stings, sunlight, stress, and certain foods. In hives or urticaria, pale red bumps or welts break out on the skin all of a sudden because of the inflammation and accumulation of fluid under the skin (46).

3. Systemic

  • Anaphylaxis: It is a severe allergic reaction to food, medication, or venom from insect stings. In the case of anaphylaxis, the immune system overreacts and causes a full-body allergic reaction. It can cause rash, slurred speech, confusion, nausea, low pulse, and shock, also called anaphylactic shock that can be fatal (47).
  • Inflammation: Inflammation is your body’s process of dealing with outside invaders such as bacteria and viruses which are considered harmful. Acute inflammation usually resolves in two weeks while chronic inflammation is linked to autoimmune disorders (48).

Read more:

Part 2: Symptoms of allergies

Part 3: Diagnosis of Allergies

Part 4: Treatments and care for allergies