First-generation immigrants face numerous challenges when adapting to new cultures: language barriers, discrimination, invalid credential recognition, and growing mental health concerns. While some of these challenges may be temporary, a long-term issue that remains unresolved within the immigrant population is the growing prevalence of allergic diseases (Lombardi, Passalaqua, and Walter Canonica 2009). Surprisingly, a potential treatment includes probiotics, as it holds promise for microbiome restoration (Yang, Liu, and Yang 2013).
Several global studies have consistently found that respiratory allergies, like allergic asthma and rhinitis, have become increasingly prevalent among migrants. A 1994 study by Leung found that migration led to increased allergy sensitivity among Asian immigrants in Australia. Immigrants were 2 times as sensitive to pollen and 1.5 times more sensitive to dust mites than their Australian-born counterparts, which correlated to greater post-migration exposure to these allergens (Leung 1994). This pattern of delayed onset is further supported by a Milan study on non-European immigrants, where 84.3% of patients (196 out of 232) reported they were healthy before migration, with allergy or asthma symptoms appearing on average 4 to 7 years after migration (Tedeshi et al. 2003). Another study conducted in Brescia, Italy, found that 60% of immigrants ( ~142 out of 237) presented with concomitant rhinitis and asthma, which was higher than the local population (40%). Rhinitis rates were generally found to be more severe in immigrants than in the native population, while asthma rates were similar (Lombardi, Passalaqua, and Walter Canonica 2009). The increased allergies in migrants across global studies highlight the crucial role of environmental shifts over genetic predisposition in allergy development (Lombardi, Passalaqua, and Walter Canonica 2009).
Traditionally, the hygiene hypothesis has been used to explain the rise of allergic diseases in Western societies, attributing it to the supposition that improved hygiene, sanitation, and modern lifestyles have led to fewer infections in infancy (Vercelli 2006). This results in a weakened type 1 T-helper (Th1) cell response, increasing susceptibility to allergies due to a dominant type 2 T-helper (Th2) response (Figure 1) (Lombardi, Passalaqua, and Walter Canonica 2009).
Th1 cells, which direct response to intracellular pathogens, produce the following cytokines: interferon-gamma (IFN-y), interleukin (IL)-2, and tumour necrosis factor (TNF)-beta. These are small proteins crucial in controlling the growth and activity of immune system cells. The cytokines activate macrophages and are responsible for cell-mediated immunity and phagocyte-development protective responses (Romagnani 1999). A Th1-dominant reaction is vital for fighting infections, but can contribute to autoimmune diseases when overactive macrophages and cytotoxic T cells attack healthy tissues. A weakened Th1 response increases susceptibility to infectious and neoplastic disease, enhancing Th2 cell levels (Marshall et al. 1998).
TH2 cells, which direct a response to extracellular pathogens, produce IL-4, IL-5, and IL-13, which are responsible for antibody production in wound healing and parasite defence (Romagnani 1999). A dominant TH2 response can lead to allergies and asthma attacks as the immune system mistakenly treats harmless substances like pollen, dust, and food proteins as both threats and triggers (Koyasu and Moro 2011). The production of IL-4 and IL-13 activates white blood cells known as B cells to create antibodies like Immunoglobulin E (IgE). Mast cells, immune cells found in loose connective tissue throughout the body, are activated by IgE, releasing histamine. Histamine is a naturally occurring chemical in the body that triggers common allergy symptoms like sneezing, itching, and swelling (Fong and Crane 2025; Holt et al. 2008).
According to the hygiene hypothesis, the development of allergies can be prevented by a shift from Th2 dominance to Th1, restoring the Th1/Th2 balance (Lombardi, Passalaqua, and Walter Canonica 2009). During early childhood and the prenatal period, this can be induced by gradual exposure to immune stimulants like viruses, bacteria, and endotoxins. However, because migrants often move from microbiome-rich environments (i.e. developing regions and rural areas) to urban settings with lower microbial diversity, they undergo a sudden and permanent change in lifestyle and environment, which impacts the restoration techniques of the Th1/Th2 balance (Lombardi, Passalaqua, and Walter Canonica 2009). These immune responses disproportionately impact migrants due to the sudden environmental and lifestyle changes; hence, a solution is vital to ease their transition to a new environment and mitigate life-altering health concerns.
A post-migration gut microbiome probiotic could expose migrants to beneficial microbes that regulate immune tolerance (analogous to early childhood microbial exposure) (Vijayan et al. 2024). However, there is currently no research done on immigrant populations for possible treatment plans. Current evidence targeted adults with allergic rhinitis, utilizing a strain of the bacteria, Lactobacillus, and found that it downregulated IL-5, IL-8, and IL-10 (Yang, Liu, and Yang 2013). Likewise, another study reported that Lactobacillus rhamnosus GG and Lactobacillus gasseri partly downregulated the Th2 immune response (Yan and Polk 2012). Many other studies focused on the prevention of allergic diseases using probiotics with various bacterial strains amongst children, infants, and adults, and found it effective (Lopez-Santamarina et al. 2021). More research on the immigrant population is required. While current evidence shows that administering probiotics containing Lactobacillus within 3-5 years of migration may reduce susceptibility to allergic diseases, targeted research is essential on immigrant populations to alleviate migration-attributed diseases.
Global immigrant experiences warrant acute attention, with increasing rates of allergic diseases posing a significant health concern. Implementing gut microbiome interventions during the first 4-7 years after migration could aid in rebalancing Th1/Th2 regulation, thereby promoting healthier immune responses in migrants. Targeted research regarding efficacy in immigrants, the most effective bacterial strain, duration of treatment, and long-term effects is still required. Nonetheless, this avenue of research is promising for alleviating one of the many challenges first-generation immigrants face.
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