Child Allergy — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Allergic diseases represent the most common chronic conditions in childhood, collectively affecting up to 40% of children worldwide. They encompass food allergy (6-8% of children), atopic dermatitis/eczema (15-20%), allergic rhinitis (10-30%), and asthma (5-15%). The 'atopic march' describes the characteristic progression of allergic disease through childhood: infantile eczema is often the first manifestation, followed by food allergy, then allergic rhinitis, and finally asthma — though not all children follow this sequence. The prevalence of childhood allergy has doubled over the past 30 years in high-income countries, attributed to reduced microbial exposure (hygiene hypothesis), dietary changes, reduced time outdoors, and rising air pollution. The most common food allergens in children are cow's milk, hen's egg, wheat, soy, peanuts, tree nuts, fish, and shellfish — the 'big eight' (or 'big nine' including sesame in the USA).

Childhood allergies result from dysregulated immune responses — failure of normal immune tolerance to harmless environmental proteins. The immune system mounts an IgE-mediated response (type I hypersensitivity) to allergens through prior sensitisation, then triggers mast cell and basophil degranulation with re-exposure. Risk factors for developing allergy: genetic predisposition — one atopic parent gives 30-40% risk; two atopic parents gives 60-80% risk; early childhood skin barrier dysfunction (eczema) allows allergen sensitisation through disrupted skin (epicutaneous sensitisation pathway); reduced microbial diversity in the infant gut microbiome (caesarean delivery, antibiotic exposure, formula feeding, urban living); delayed or avoided introduction of allergenic foods during weaning (the 'old advice' — now reversed); tobacco smoke exposure increases asthma and eczema risk; and pet ownership paradoxically reduces allergy risk if exposure occurs from birth (the 'old friends' hypothesis). Formula-fed infants have higher food allergy risk than exclusively breastfed infants.

Food allergy: symptoms typically develop within minutes to 2 hours of ingestion. Mild-moderate: urticaria (hives), perioral and facial swelling, vomiting, abdominal pain, diarrhoea, and rhinitis. Severe (anaphylaxis): throat tightening, stridor, wheeze, severe breathlessness, hypotension, pallor, collapse, and loss of consciousness — a life-threatening emergency requiring immediate adrenaline (epinephrine). Atopic eczema: itchy, dry, red, scaling rash — typically on the face and scalp in infants, behind the knees and elbow creases in older children; chronic scratching leads to skin thickening (lichenification). Allergic rhinitis: nasal congestion, rhinorrhoea, sneezing, and itchy eyes — causing sleep disturbance and school performance impairment. Asthma: recurrent wheeze, cough (especially nocturnal), chest tightness, and breathlessness triggered by exercise, cold air, viral illness, and allergen exposure. Food protein-induced enterocolitis syndrome (FPIES): non-IgE-mediated reaction — profuse repetitive vomiting 1-4 hours after ingestion, without skin or respiratory symptoms.

A detailed clinical history is the cornerstone of allergy diagnosis in children — timing of reaction, foods or triggers involved, symptom types, and resolution. Skin prick testing (SPT): the primary allergy diagnostic test — performed by a specialist; results available in 15 minutes; positive if wheal 3 mm or more above negative control; must be interpreted in clinical context (sensitisation without clinical allergy occurs). Specific IgE blood testing (ImmunoCAP): useful when SPT is not feasible (widespread eczema, young infants, antihistamine use); individual allergen components (e.g., Ara h 2 for peanut anaphylaxis risk) improve specificity. Oral food challenge (OFC): the gold standard for confirming or excluding food allergy when history or tests are equivocal — performed under medical supervision with resuscitation equipment available. Patch testing (epicutaneous): for suspected delayed (non-IgE) contact allergy. Spirometry with bronchodilator response and peak flow variability diagnose asthma. Skin biopsy is not routinely needed for eczema diagnosis. Blood eosinophil count and total IgE support atopic diagnosis but are not diagnostic alone.

Food allergy management: strict avoidance of the causative allergen(s) — requires comprehensive education for parents, caregivers, and school staff; careful label reading (pre-packaged food labelling laws require declaration of the 14 major allergens); school and nursery management plans. Adrenaline auto-injectors (AAIs — EpiPen, Jext, Emerade): prescribed for all children with a history of anaphylaxis or at high risk — must be carried at all times by two AAIs; parents and caregivers must be trained in their use; replaced before the expiry date. Antihistamines: cetirizine (non-sedating) or loratadine for mild allergic reactions, urticaria, and allergic rhinitis — not adequate for anaphylaxis. Oral immunotherapy (OIT) for peanut allergy: FDA-approved palforzia (peanut flour AR101) for children 4-17 years — desensitises through gradual exposure under specialist supervision, significantly increasing the threshold dose for reaction. Eczema: emollients (at least twice daily, prescribed in large quantities — 250-500g monthly) are the cornerstone; mild to moderate topical corticosteroids (hydrocortisone 1%, betamethasone); calcineurin inhibitors (tacrolimus, pimecrolimus) for facial or sensitive skin; dupilumab (anti-IL-4Rα) is approved for moderate-severe atopic dermatitis in children from 6 months. Asthma: stepwise GINA-based approach — inhaled salbutamol (SABA) for acute relief; low-dose inhaled corticosteroid (ICS) for persistent asthma; add LABA, LTRA, or biologics (mepolizumab, dupilumab, omalizumab) for severe asthma.

Anaphylaxis untreated with adrenaline (epinephrine) causes respiratory arrest, cardiovascular collapse, and death within minutes — the most severe complication of IgE-mediated allergy to food, insect venom, or latex. Uncontrolled atopic eczema causes chronic sleep deprivation (affecting 60-80% of children from pruritus), secondary bacterial skin infections (Staphylococcus aureus colonises over 90% of eczema skin), and psychosocial impairment of school performance and development. Undertreated allergic asthma causes airway remodelling with irreversible airflow limitation. Severe allergic rhinitis impairs sleep quality, school performance, and significantly worsens asthma control by increasing lower airway inflammation — supporting the 'one airway, one disease' concept requiring simultaneous management of nasal and bronchial disease.

Early introduction of allergenic foods — particularly peanuts and egg — from 4-6 months of age (as complementary foods are introduced) significantly reduces food allergy development: the LEAP trial demonstrated 80% reduction in peanut allergy when peanut was introduced early in high-risk infants with eczema or egg allergy. Current UK and international guidelines recommend early introduction of all allergenic foods from 4-6 months, including peanut, egg, milk, wheat, and fish, regardless of family history. High-risk infants (severe eczema or egg allergy) should have specialist allergy assessment before peanut introduction. Emollient therapy from birth: several randomised trials (BEEP, STOP-AD) suggest daily emollient application may reduce eczema incidence by improving skin barrier function — though recent large trials have been mixed. Exclusive breastfeeding for at least 4-6 months supports gut microbiome development. Vitamin D supplementation in pregnancy and infancy may reduce allergy and asthma risk — evidence is emerging.

Seek immediate emergency care (call 999/112/911) for any suspected anaphylaxis in a child: throat swelling, stridor, severe wheeze, collapse, pallor, or loss of consciousness after allergen exposure — administer adrenaline auto-injector immediately and call emergency services. Do not wait. See a GP promptly if your child develops an allergic reaction after eating a specific food, develops a persistent itchy rash (possible eczema), has recurrent wheeze or cough (possible asthma), or has persistent nasal symptoms. Seek specialist paediatric allergy referral if: a child has been prescribed an adrenaline auto-injector (requires allergy review and anaphylaxis action plan), food allergy is complex or multiple foods are implicated, eczema is not controlled by first-line treatments, or when food reintroduction ('growing out' of allergy) needs to be assessed formally by an oral food challenge.