The Increasing Threat of Allergic Disease

According to Allergy UK, 21 million Brits are affected by allergies. Allergic disease can take many forms, including asthma, hay fever, eczema, and dietary allergies. All are the result of an overreaction of the immune system to an otherwise harmless substance, whether that be dust, pollen, or certain foods. The most common allergies are typically established from the very first exposure to the offending substance and involve the immune system creating a type of antibody called immunoglobulin E (IgE). The IgE produced is highly specific to the allergen and catalogued in the body’s immunological memory such that, in the event of another exposure, the immune system would respond rapidly and aggressively to eliminate the foreign substance.

Although this is an essential mechanism for human survival — allowing us to defend ourselves against harmful bacteria and viruses — an excessive immune reaction to something which does not actually pose a risk can cause self-inflicted damage. While symptoms of mild allergic disease may include a runny nose, itching, breathing difficulties, and watery eyes, life-threatening anaphylactic shock can occur in the most severe cases. The onset of anaphylaxis is fast and often involves plummeting blood pressure and sudden swelling of the throat or tongue, which blocks the airways. It occurs when re-exposure to a particular allergen triggers the release of high levels of histamine, which flood the body and cause blood vessels to leak fluid into neighbouring tissues.

According to the Medicines and Healthcare Products Regulatory Agency, 25,721 people were admitted to hospital due to anaphylaxis in 2022-23 in the UK. This represents a 108% increase on the 12,631 admissions previously reported in 2002-03 and is illustrative of a growing problem across the globe. The World Health Organisation has recognised allergic disease as a public health crisis, estimating that 400 million people are suffering from asthma in 2025, with a 10–40% allergy prevalence by country. 

Although multiple different factors may be driving the global increase in allergic disease, a large part of it can be attributed to the urbanised environment and lifestyle in which humans now live. One theory, called the “Old Friends” hypothesis, suggests that humans have become less exposed to beneficial microorganisms, which, throughout evolutionary history, stimulated the regulation of the mammalian immune system. Indeed, antibiotic usage in childhood — which reduces the levels of such microorganisms inside the body — is connected to allergy development later in life. Industrial air pollution may also play a role by damaging the respiratory system, while global warming has contributed to longer periods of elevated pollen levels. 

It has also been suggested, although not fully confirmed, that a vitamin D deficiency is correlated with the risk of allergic disease. Certainly, missing out on sun exposure (which boosts natural vitamin D production) is a huge problem in the UK, with adults spending around 90% of their time indoors due to office-based or work-from-home jobs and the widespread popularity of streaming platforms, social media, and online gaming. 

Although the anaphylaxis hospitalisations have increased, the case fatality rate of food-induced anaphylaxis has thankfully remained stable over 1998-2018. However, it is not clear if this consistency is linked to the 336% increase in adrenaline autoinjector prescriptions over the same period. Nevertheless, increasing public knowledge and awareness surrounding allergies and what to do in the event of an allergic reaction is a growing need that must be met.

Guidance from the NHS states: “If you or someone you're with is having a serious allergic reaction and has an adrenaline auto-injector (such as an EpiPen), you should use it immediately. Instructions are included on the side of the injector if you forget how to use it or if someone else needs to give you the injection. Call 999 for an ambulance after using the injector, even if you or the person you're with seems to be feeling better.”

Image from Wikimedia Commons