Allergy: An itch that goes around the world All over the world, allergies are counted as one of the most common chronic diseases that impact millions of people every day. What makes them so common is the fact that they are an umbrella term for a plethora of diseases with different subtypes and affecting different organs: allergic rhinitis or inhalant allergy (eyes, nose, and airways), allergic asthma (lungs and airways), food allergy (mouth, skin, and systematic symptoms), eosinophilic esophagitis (respiratory and digestive tract), anaphylaxis (systematic symptoms), atopic dermatitis (skin), insect allergy (skin and systematic symptoms), and drug allergy (systematic symptoms). Due to the overwhelming data for all those allergy-related diseases, we will focus on allergic rhinitis or inhalant allergy, food allergy, and drug allergy in this blog. Allergic rhinitis According to the American Academy of Allergy, Asthma & Immunology, allergic rhinitis affects 10% to 30% of the population worldwide. 1 In a recent cross-sectional and multicentred study, the prevalence of allergic rhinitis was 8% (children), 24% (adolescents), and 10% (adults) in India. 2 Savouré et al. (2022) shared detailed information about the prevalence of allergic rhinitis all over the world. (Fig. 1). 3 Food allergy A European multicentre study from eight Western countries concluded that 1%-4% of school children suffer from food allergies. 4 The prevalence rate of food-specific IgE sensitisation for at least one food allergen was 19.1% in Indian children, although true food allergy was only proven in 0.14% of them. 5 Furthermore, Warren et al. summarised the prevalence of food allergies around the globe (Tab. 1). 6 Continent Prevalence of food allergies Age groups North America 3.5–7.6% (Canada, Mexico, and USA) 0-17 years Europe 1.7–9.3% (Austria, Belgium, Croatia, Denmark, Finland, France, Germany, Greece, Greenland, Iceland, Italy, Malta, Netherlands, Norway, Poland, Portugal, Slovenia, Sweden, Switzerland, and the UK) 0-20 years Central and South America 0.6–5.5% (Brazil, Chile, and El Salvador) 4 months–15 years Middle East 0.8–8 % (Israel, Kuwait, Lebanon, Turkey, and the UAE) 0-30 years Africa 2–5% (Ghana and South Africa) 1–16 years Asia, and Oceania 1.1–7.7% (Australia, China, Hong Kong, Japan, Singapore, South Korea, Taiwan, Thailand) 0-18 years Drug allergy The World Allergy Organization (WAO) defines drug allergy as ‘an immunologically mediated drug hypersensitivity reaction, which can be either IgE or non-IgE mediated’.  It is generally very uncommon, representing less than 10% of all adverse drug reactions. However, approximately 3%-6% of all hospital admissions are related to adverse drug reactions, and 10%-15% of people admitted to the hospital suffer from them. 7 A recent Polish study gave insight into common culprit drugs for adverse reactions: NSAIDs (67.5%), followed by antibiotics (54.3%), local anaesthetics (7.4%), general anaesthetics (2%), and other drugs such as antihypertensive drugs (4.6%), dietary supplements (3.2%), antihistamines (2.8%), and contrast agents (2.4%). 8 For decades, doctors and healthcare workers have noticed an increase in the prevalence of allergies. Numerous scientists have tried to investigate the reasons for this persistent rise and come up with different explanations. The “hygiene hypothesis” is generally accepted and states that exposure to germs and infections during childhood helps to “educate” the immune system. Therefore, a very clean and sterile environment would be counterproductive, as there are no stimuli for the immune system. This is directly linked with the idea of the “biodiversity hypothesis”, which highlights the importance of a diverse microbiome as it seems to promote immune balance and protect from allergy and inflammatory disorders. 9,10 Furthermore, lifestyle changes, such as the increase of pollution in the environment (“pollution hypothesis”), were considered a reasonable explanation. Studies found a direct correlation between diesel exhaust and increased airway inflammation, allergies, and asthma exacerbations. 11,12 Along with that, psychosocial factors, such as increased stress and fast-paced lifestyles, were also found to be accountable for an increased allergy prevalence. For all those reasons, allergies have been called the “epidemic of the 21st century”. 13 What you should know about Allergy: Symptoms, Diagnosis, and Treatment Allergy is often referred to as an overreaction of the immune system since it attacks normally harmless substances. The mechanism behind allergies is well-understood, and scientists agree that IgE antibodies are the culprits that cause allergic reaction. 14 The symptoms can be diverse, according to the allergy-related disease: For allergic rhinitis, common symptoms are a running or blocked nose, sneezing, wheezing, and itchy and swollen eyes. For food allergies, itchiness in the mouth, rashes, diarrhea, vomiting, dizziness, and headaches are typical symptoms. However, some allergies, such as food and drug allergies, also lead to life-threatening anaphylaxis, where the body’s circulatory system and breathing drop abruptly due to the systemic allergic reaction. 14,15 There are different types of allergies according to the offensive allergen: plant and tree pollen, house dust mites, mold spores, and pet hair (dog, cat, etc.) are the most common inhalant allergens 16, whereas milk, eggs, fruits (peaches and apples), nuts, wheat, soy, sesame, and seafood (shrimps and fish) tend to be the most prevalent food allergens 17. The onset of these allergies depends on the exposure; a European study found that shrimp allergies were one of the most common food allergies in Spain and Iceland, which are countries with the highest seafood consumption. 17 Another influencing factor is age. Children usually suffer from milk allergies from an early age, but they can develop tolerance, which is why fewer individuals have a milk allergy in adulthood. 18 The most common method to diagnose allergies is skin prick testing, where allergen extracts are applied subcutaneously or intradermally, and the reaction is read after a short time. Redness and wheal formation are positive signs for the test. Additionally, in-vitro tests are available where only the patient’s blood is needed. The levels of allergen-specific IgE antibodies are quantified with different methods, and higher levels of allergen-specific IgE confirm allergy. 19 However, for food allergies, the double-blind, placebo-controlled, food challenge is the gold standard, where the assumed culprit food is given to the patient in a safe setting and the reaction is monitored. Newer and safer methods, such as basophil or mast