Children's Allergies: A Nutritional and Natural-Health Reference
1. Definition and Overview
A child's allergy is an immune system reaction to a foreign substance, or allergen, that is considered harmless to most. The most accepted definition describes food allergy specifically as an adverse immune response to food proteins that occurs in a susceptible host; its manifestations are not dose-dependent but are reproducible. More broadly, allergies are reactions that are usually caused by an overactive immune system, and these reactions can occur in a variety of organs in the body, resulting in diseases such as asthma, hay fever, and eczema.
Allergic diseases in children have increased significantly in recent years and now affect up to 35% of children, and they are a major cause of morbidity. Atopic diseases — including atopic dermatitis (AD), food allergy (FA), allergic rhinitis (AR), and asthma — are the most common chronic conditions in childhood and adolescence, affecting up to 30% of the global population.
2. Immunological Mechanisms and Body Systems Involved
2.1 The IgE-Mediated Pathway
The body attacks allergens with antibodies called immunoglobulin E (IgE). These antibodies are attached to special cells called mast cells, and allergens stick to the antibodies. This makes the mast cells release histamine and other chemicals, causing an allergic reaction. Visible allergy symptoms are the body's reaction to inflammatory chemicals, such as histamines, cytokines, or leukotrienes, which are released from white blood cells to fight foreign substances in the body.
Activation of the T-cell by an allergen leads to the production of cytokines which promote maturation of the B-cell into a plasma cell that produces IgE. The cytokines IL-4 and IL-13 are especially important in this respect.
2.2 Broader Immune Complexity
The five components of the immune system — the epithelium, innate immune cells, T cells, B cells, and effector cells (mast cells, eosinophils, and basophils) — can either promote tolerance to food antigens or sensitization to them, which will then lead to allergic manifestations. Allergic reactions occur when the body's immune system responds to a harmless substance as if it were a toxin or a foreign invader. This overactive response can be caused by one of several different types of immune mechanisms and can involve virtually any organ or multiple organs in the body.
2.3 Body Systems and Organs Affected
An allergic reaction can happen anywhere in the body, including the skin, eyes, lining of the stomach, nose, sinuses, throat, and lungs — places where immune system cells are found to fight off germs that are breathed in, swallowed, or come in contact with the skin.
- Skin: Skin involvement includes perioral skin rashes, atopic dermatitis, urticaria, and angioedema.
- Respiratory System: Respiratory involvement includes cough, stridor, and wheezing. When mast cell activation happens in the lungs' breathing tubes, it can cause asthma symptoms, such as coughing and wheezing.
- Nasal Passages and Eyes: Allergic rhinitis is a chronic, non-infectious inflammatory response of the nasal mucosa caused by exposure to allergens, manifested by symptoms such as itchy nose, sneezing, runny nose, and nasal congestion.
- Gastrointestinal Tract: During early life, immature mucosal defenses permit the increased absorption of allergens, which act on an immature immune system. In infants, the main exposure is to food allergens, whereas in older children, it is to inhalant allergens.
- Systemic (Anaphylaxis): Anaphylaxis is the term used to refer to an allergic reaction that is life threatening and involves multiple organ systems.
3. The Atopic March
Cross-sectional and longitudinal studies have indicated that allergic diseases occur in a time-based order: from atopic dermatitis and food allergy in infancy to gradual development into allergic asthma and allergic rhinitis in childhood. This phenomenon is defined as the "atopic march." In terms of anatomic structure, it follows the spatial evolution of skin–gastrointestinal tract–respiratory tract.
Atopic dermatitis (AD) is an inflammatory disease characterized by pruritic skin lesions. The pathogenesis of AD may include disrupted epidermal barrier function, immunodysregulation, and IgE-mediated sensitization to food and environmental allergens. AD is also part of a process called the atopic march, a progression from AD to allergic rhinitis and asthma.
The estimated odds risk for the association of eczema at 2 years with asthma at 6 years is about 1.80. Additionally, approximately 70% of patients with severe AD develop asthma compared to 20–30% of patients with mild AD and approximately 8% of the general population. However, the atopic march is not universal: findings from birth cohort studies showed that one in four children with eczema transitioned to at least one allergic phenotype, and one in five transitioned to multimorbidity (having all three conditions).
Similar predisposition factors, inflammation patterns, and triggers in the upper and lower airways suggest the concept of "one airway, one disease." Allergic rhinitis has been identified as a comorbidity of asthma and a risk factor for asthma occurrence and exacerbation.
4. Contributing and Associated Factors
4.1 Genetic Predisposition
Although there is a genetic predisposition, it is the exposure to environmental allergens, irritants, and infections that will determine the sensitization to different dietary and inhalant allergens. If one parent has allergies, there's a 25% chance that a child will also be allergic. The risk is more than doubled to 60%–70% if both parents have allergies.
Markers of skin barrier dysfunction were associated with food allergy risk. Increased skin transepidermal water loss (OR, 3.36) and filaggrin gene loss-of-function variants (OR, 1.93) were linked to higher odds of food allergy development.
4.2 Prior Atopic Conditions
Prior allergic conditions were among the most strongly associated risk factors. Atopic dermatitis within the first year of life was associated with nearly fourfold higher odds of developing food allergy (OR, 3.88). Allergic rhinitis (OR, 3.39) and wheezing (OR, 2.11) were also associated with increased risk.
4.3 Environmental and Lifestyle Factors
Risk factors currently under investigation include genetic atopic predisposition, early childhood allergen exposure and sensitization, occurrence of viral respiratory infections in young children, maternal smoking during pregnancy, poor dietary factors, lack of breastfeeding, childhood obesity, having a certain immunologic predisposition (Th2-prone), air pollution, and frequent immunizations in childhood.
4.4 Mode of Delivery and Early Microbial Exposure
Gestational age and the mode of delivery have a huge impact on gut microbiome (GM) composition. Preterm birth and cesarean section are linked to the development of allergic conditions. Vaginally delivered infants encounter the maternal vaginal and fecal microbiota, resulting in neonatal gut colonization by vagina-associated microbes such as Lactobacillus. In contrast, cesarean section-delivered infants are not directly exposed to maternal microbes and are more likely to become colonized by environmental microorganisms from the maternal skin or hospital environment.
An association exists between cesarean section as the mode of delivery and the increased risk of pediatric allergic rhinitis, and cesarean section is a risk factor for allergic rhinitis.
4.5 The Hygiene Hypothesis and Microbial Diversity
The hygiene hypothesis, initially proposed by David Strachan in 1989, posits that exposure to mild infections in early life can have a protective effect against allergic diseases. Pre- and postnatal exposure to pets, vaginal birth, and childhood spent in rural environments reduce the risk of developing allergic diseases. Having siblings in early life significantly reduces the risk of developing food allergy, a protective effect mediated by accelerated gut microbiota maturity, characterized by higher microbial alpha diversity and increased short-chain fatty acids (SCFAs) such as acetate and butyrate.
4.6 Gut Microbiome Dysbiosis
The relationship between the human microbiome and food allergies in children is complex and multifactorial. The gut microbiome plays a crucial role in the formation of the immune system, and alterations in the microbial community can increase the risk of developing food allergies. The gut microbiome has been shown to play a part in the development of asthma, atopic dermatitis, and food allergies through mucosal tolerance and possible bacterial metabolites over the past decade.
The type of infant feeding (breastfeeding vs. formula feeding) and the diet after weaning play a crucial role in modulating the structure and function of the gut microbiome. The housing setting, increased hygiene, and the presence of siblings and pets can also modulate gut microbiome composition.
5. Nutrients, Herbs, and Natural Ingredients
5.1 Vitamin D
Scientific Evidence
In addition to traditional functions in calcium and phosphate homeostasis, vitamin D modulates a variety of processes, and evidence shows that it has an important role in different allergic diseases such as asthma, atopic dermatitis, and food allergy. Vitamin D shows wide effects in key functions of the immune system, due to the presence of vitamin D receptors in most cells of the human body.
Most, but not all, studies have shown that low vitamin D levels increase the risk for asthma and allergies, but a few suggest an increased risk with high levels. Vitamin D deficiency was significantly more frequent in the group of children with an allergic disease than in the control group (p = 0.007). Statistically significantly higher vitamin D concentrations in blood were observed in the group of children with a mild course of the disease compared to children with a severe clinical course (p = 0.03).
Recent evidence suggests that low blood vitamin D level is a risk factor for food allergy; vitamin D deficiency predisposes to gastrointestinal infections, which may promote the development of food allergy. Vitamin D can prevent the intestinal immune system from being exposed to allergens by maintaining the integrity of the mucosal barrier.
A systematic review and meta-analysis of RCTs found that vitamin D supplementation significantly reduced Scoring Atopic Dermatitis or the Eczema Area and Severity Index scores in children with atopic dermatitis compared with placebo (standard mean difference = −0.5, 95% CI: −0.87 to −0.12, p = 0.009). A population-based study of 5,276 one-year-old infants found that infants of Australian-born parents with vitamin D insufficiency (≤50 nmol/L) were more likely to be peanut (aOR, 11.51) and/or egg (aOR, 3.79) allergic than those with adequate vitamin D levels, independent of eczema status.
Evidence strength: Several data suggest that serum 25-hydroxyvitamin D levels are often insufficient in children with asthma, atopic dermatitis, and food allergy. Further clinical trials are needed to provide conclusive evidence and to identify the effects of vitamin D in allergic diseases. Many clinical studies believe that vitamin D supplementation can improve infants' and children's food allergy, however, some show negative results or opposite results. Overall, evidence is suggestive but not yet definitive; optimal dosing ranges remain undefined.
5.2 Omega-3 Polyunsaturated Fatty Acids (PUFAs)
Scientific Evidence
Polyunsaturated fatty acids (PUFAs) are involved both in immune system regulation and inflammation. Within the PUFAs category, omega-3 (ω-3) may reduce inflammation, whereas omega-6 (ω-6) PUFAs are generally considered to have a proinflammatory effect. Recent evidence highlights an imbalance in the ω-3:ω-6 ratio with an increased intake of ω-6, as a consequence of the shift towards a westernized diet.
Early omega-3 fatty acids exposure can influence early immune development and potentially prevent allergic disease. A systematic review and meta-analysis of RCTs found that omega-3 supplements during pregnancy may reduce the risk of asthma or asthma symptoms during childhood, but the evidence is limited. No conclusions could be drawn for effects on other atopic diseases or for effects of supplementation during lactation or infancy.
There is limited evidence to support omega-3 fatty acids during childhood could reduce the risk of allergic disease. More high-quality research is needed to clarify if and how omega-3 supplements during pregnancy or infancy reduce risk of asthma or allergies during childhood.
Evidence strength: Preliminary and mixed. Most systematic reviews describe limited evidence for postnatal supplementation; prenatal omega-3 may offer some protection against asthma, but findings are inconsistent across trial designs.
5.3 Probiotics
Scientific Evidence
Growing evidence underlines the pivotal role of infant gut colonization in the development of the immune system. The possibility to modify gut colonization through probiotic supplementation in childhood might prevent atopic diseases.
A systematic review of 29 RCTs found that probiotics reduced the risk of eczema when used by women during the last trimester of pregnancy (RR, 0.71), when used by breast-feeding mothers (RR, 0.57), or when given to infants (RR, 0.80). Evidence did not support an effect on other allergies, nutrition status, or incidence of adverse effects.
Probiotic supplements are reported to be effective in the prevention of eczema, while proof of clinical efficacy in food allergy is still lacking. With respect to allergic rhinitis, probiotics did not significantly reduce the odds of AR at any age (≤1 year: ORp = 0.73, P = 0.17; >1 year: ORp = 0.95, P = 0.46), and early-life gut microbial colonization is crucial for immune system development, but the efficacy of probiotic interventions during pregnancy or infancy in preventing allergic rhinitis remains unclear.
Some meta-analyses have demonstrated the preventive and therapeutic effects of probiotics in children with allergic diseases such as atopic dermatitis and eczema. However, other meta-analyses have failed to prove their preventive effect in developing asthma or wheezing in children. No conclusive evidence exists regarding the effects of probiotics on children with allergic rhinitis.
Probiotic strains studied include Bifidobacterium, Lactobacillus, Enterococcus, Escherichia, and Clostridium butyricum strains, with treatment durations ranging from 3 weeks to 39 months.
Evidence strength: Moderate for eczema prevention; weak-to-absent for other allergy types. Strain specificity, timing of administration, and population heterogeneity limit firm conclusions.
5.4 Quercetin
Traditional Use
Quercetin is a flavonoid naturally present in a wide range of foods including onions, apples, berries, and leafy greens, and has a long history of use in traditional herbal medicine systems — particularly in Traditional Chinese Medicine (TCM), where plant combinations containing quercetin-rich herbs such as Ginkgo biloba have been used for respiratory and inflammatory conditions. Quercetin is the most abundant dietary flavonoid, present in a wide range of fruits, vegetables, and beverages.
Scientific Evidence
Quercetin inhibits mast cell degranulation, reduces the production of histamine and pro-inflammatory cytokines, and restores homeostasis of the immune system by modulating the Th1/Th2 and Treg/Th17 balances. Additionally, its antioxidant properties help to dampen oxidative stress, a critical factor in the pathophysiology of allergic diseases.
In vitro studies have consistently demonstrated quercetin's ability to suppress allergic reactions. In vivo studies, particularly in murine models of allergic rhinitis, have confirmed its efficacy in relieving symptoms such as nasal itching, sneezing, rhinorrhea, and congestion. Preclinical evidence also supports its therapeutic potential in asthma, conjunctivitis, atopic dermatitis, and food allergies. However, human studies are still scarce, as only two clinical trials have investigated quercetin as a monotherapy.
One small clinical study enrolled 58 patients with allergic asthma and allergic rhinitis, finding that subjects supplemented with quercetin phospholipids (100–200 mg/day) plus standard management showed a more significant decrease in daily symptoms and night symptoms, a better improvement in peak expiratory flow/FEV1, and an improvement in PEF variability compared with subjects receiving standard management only.
Evidence strength: Primarily preclinical (in vitro and animal models). Human clinical trial data are very limited and not yet replicated in pediatric-specific populations. Results from the few small trials are promising but insufficient for definitive conclusions.
5.5 Butterbur (Petasites hybridus)
Traditional Use
Butterbur is a plant extract from a shrub that grows in Asia, Europe, and some parts of North America. People have traditionally used butterbur to treat migraine and hay fever (allergic rhinitis).
Scientific Evidence
According to the NCCIH, a 2007 study found that butterbur may have antihistamine effects and may be beneficial for allergic rhinitis. Most clinical research on butterbur has been conducted in adults and has not been specifically validated for children. Evidence in the pediatric population remains very limited.
Evidence strength: Limited; adult-focused. There are no robust pediatric-specific clinical trials. Butterbur extracts containing pyrrolizidine alkaloids carry hepatotoxicity risk and should only be used in PA-free certified preparations; no safety data exists for children.
5.6 Traditional Chinese Herbal Medicine (TCM)
Traditional Use
Chinese herbal medicine has a history spanning thousands of years of use for respiratory and immune conditions, including nasal congestion, rhinitis, and skin complaints. Traditional Chinese medicine compound has the treatment characteristic of multi-pathways, multi-links, and multi-targets, and has the potential prevention and treatment advantages.
Scientific Evidence
Clinical reports suggest that Chinese herbal medicine (CHM) is effective in allergic rhinitis treatment. Research has evaluated the clinical efficacy of Chinese herbal medicine in treating nasal itching caused by allergic rhinitis in children. A systematic review and meta-analysis comparing CHM with Western medicine found that Chinese herbal medicine holds great potential in alleviating symptoms, modulating immune factors levels, and reducing relapse in pediatric rhinitis, and CHM is relatively safe. However, the efficacy and safety of CHM in treating pediatric rhinitis still need to be confirmed due to the inclusion of studies with low methodological quality, small sample sizes, and potential heterogeneity.
Evidence strength: Preliminary and methodologically limited. Existing systematic reviews indicate potential benefit but are substantially constrained by heterogeneity and risk of bias in included studies.
5.7 Perilla Frutescens and Rosmarinic Acid
Traditional Use
Perilla frutescens is an aromatic herb used in East Asian traditional medicine (particularly Japan, China, and Korea) for respiratory and inflammatory conditions including asthma and rhinitis. It has been consumed both as food and as a medicinal preparation.
Scientific Evidence
In Perilla frutescens, 271 active compounds have been identified in the seeds, stems, and leaves, including rosmarinic acid and luteolin with anti-allergic (antihistaminic with inhibition of mast cell degranulation), antioxidant (scavenging of reactive oxygen species), and anti-inflammatory (reduction in the release of the HMGB1 protein with an inhibitory effect on pro-inflammatory cytokines TNF-α and IL-6) properties. However, well-powered, placebo-controlled pediatric trials on Perilla frutescens specifically are lacking.
Evidence strength: Preliminary; largely mechanistic or in vitro. A nutraceutical combination study incorporating Perilla frutescens, quercetin, and vitamin D3 in children with seasonal allergic rhinitis showed add-on benefit, but the study was small and compound (not allowing isolation of individual components).
6. Dietary and Lifestyle Factors
6.1 Mediterranean Diet
Several studies have linked the consumption of a Mediterranean diet in children with a lower risk of suffering from food allergies and other allergic diseases such as asthma and atopy. This is probably due to this diet's high content of non-digestible carbohydrates from the fiber contained in fruits, cereals, and legumes, which, when fermented by intestinal bacteria, produce SCFAs that protect against these allergic diseases.
The adoption of a Mediterranean-style diet, probiotics, and prebiotics may help to mitigate the risk of developing allergies, while breastfeeding is essential in establishing a diverse gut microbiome and providing critical nutrients to infants.
6.2 Western Diet and Dysbiosis
Advances in metagenomics and metabolomics implicate diet and gut microbiome (the diet-gut microbiome axis) as key modulators of the maturation of the immune system. Diet from conception (maternal diet) up to the first 24 months of age may influence the risk of developing food allergy. A recent study suggests that a healthy diet with high levels of fruits, vegetables, and home-made foods is associated with less food allergy at the age of 24 months.
6.3 Breastfeeding
The protective role of breastfeeding has a positive effect on allergy prevention, which is opposed by the early introduction of solid foods, but larger studies are needed to confirm the evidence. There is evidence that breastfeeding is effective in providing partial protection to infants. During the first year after birth, the most substantial development of the gut microbiota takes place and the relations between gut microbes and host immunity are established.
6.4 Early Allergen Introduction
Early introduction of allergenic foods in infancy has emerged as one of the more promising strategies to decrease food allergy development. The Learning Early About Peanut Allergy (LEAP) study found that early introduction of peanut into the diets of high-risk atopic infants protects against the development of peanut allergy.
All major guidelines recommend the early introduction of allergenic foods (generally at age 4–6 months, depending on the guideline and infant risk level) and continued intake once introduced. While there is evidence of increased allergy risk when solids are introduced earlier than 3 or 4 months of age, there is no evidence that delaying the introduction of allergenic foods beyond 4 months of age decreases the risk of allergies in infants in the general population.
However, the evidence does not extend equally to all interventions: many interventions attempted in pregnant or breastfeeding women and infants appear to have little to no benefit in preventing food allergy, including dietary avoidance of food allergens, vitamin supplements, fish oil, probiotics, prebiotics, and synbiotics — though it should be noted that the evidence remains uncertain in many cases.
6.5 Short-Chain Fatty Acids (SCFAs) and Gut Health
Butyrate and other SCFAs seem to play a key role in immunotolerance to food antigens, so breastfeeding and the consumption in childhood of a Mediterranean diet, rich in non-digestible carbohydrates that are transformed into butyrate in the colon, could reduce the risk of food allergies and other allergic diseases.
6.6 Omega-3:Omega-6 Dietary Ratio
Recent evidence highlights an imbalance in the ω-3:ω-6 ratio with an increased intake of ω-6 as a consequence of the shift towards a westernized diet. In critical age groups such as infants, toddlers, and young children, as well as pregnant and lactating women or fish-allergic patients, ω-3 intake may be inadequate. Results from a systematic review indicated that intakes of ω-3 and ω-6 PUFAs were largely suboptimal in specific population groups in Europe.
6.7 Asthma, Obesity, and Comorbidities
Asthma often coexists with a range of comorbidities, including both atopic (allergic rhinitis, atopic dermatitis, and food allergies) and non-atopic symptoms (anxiety, depression, gastro-esophageal reflux disease, and obesity). Childhood obesity is listed among the risk factors under active investigation for contributing to allergic disease development.
6.8 Environmental and Lifestyle Modifiers
Atopic conditions frequently coexist and share common genetic, environmental, dietary, and microbial risk factors. Triggers include environmental factors such as allergens (house dust mites, pollen, pet dander, and mold), viral infections, smoke exposure, and air pollutants. Although allergies can develop at any age, they most commonly show up during childhood or early adulthood.
References
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