Skin Allergy — Symptoms, Causes & Treatment | MyMedicPlus

Skin allergies are a diverse group of cutaneous hypersensitivity reactions in which the immune system mounts an abnormal or exaggerated response to a substance that would be harmless in a non-sensitised individual. They collectively represent some of the most common immunological conditions encountered in clinical practice, affecting approximately 15-20% of the global population at some point during their lives. The three most clinically significant types are: allergic contact dermatitis (ACD) — a delayed-type (Type IV, T-cell mediated) hypersensitivity reaction characterised by localised inflammation at the site of skin contact with a causative allergen, appearing 24-96 hours after exposure; urticaria (hives) and angioedema — immediate-type (Type I, IgE-mediated) hypersensitivity reactions causing transient wheals and/or deeper subcutaneous tissue swelling within minutes of allergen exposure; and atopic dermatitis (eczema) — a chronic, relapsing, Type 2 immune-mediated inflammatory skin condition driven by skin barrier dysfunction, IgE sensitisation, and Th2 cytokine overactivation (IL-4, IL-13, IL-31), affecting 15-20% of children and 5-10% of adults. Additional types include photoallergic contact dermatitis (UV-activated allergens in sunscreens or medications) and drug hypersensitivity exanthems (morbilliform rashes from antibiotics, anticonvulsants). Severity spectrum ranges from mild, self-limiting localised rashes to potentially fatal systemic anaphylaxis requiring immediate adrenaline — making accurate allergy diagnosis, allergen identification, and risk-stratified management essential. The atopic triad (atopic dermatitis, allergic rhinitis, and asthma) frequently co-exists in genetically predisposed individuals.

Allergic contact dermatitis (ACD) triggers: nickel (the most common contact allergen worldwide — found in jewellery, belt buckles, watch straps, metal clasps, and phone cases — responsible for up to 20% of positive patch tests in European dermatology centres); fragrances (second most common class — found in cosmetics, personal care products, perfumes, air fresheners, and topical medications; fragrance mix I and II detect most but not all fragrance sensitisations); preservatives (methylisothiazolinone — MI and MCI — widely used in cosmetics and household products; caused a European epidemic of contact allergy in the 2010s before regulatory restrictions; parabens; formaldehyde-releasing preservatives); latex (from natural rubber products — surgical and examination gloves, condoms, balloons — particularly important in healthcare workers with 5-17% sensitisation); para-phenylenediamine (PPD — hair dye ingredient; strong sensitiser; cross-reacts with local anaesthetics, sulfonamides, and azo dyes); and plants (urushiol from poison ivy, oak, and sumac — the most potent plant contact allergen in North America; teakwood and other occupational allergens). Urticaria and angioedema triggers: foods (peanuts, tree nuts, shellfish, fish, milk, eggs — IgE-mediated; onset within 5-30 minutes of ingestion); NSAIDs (aspirin, ibuprofen — both IgE-mediated for some and pharmacological pseudo-allergy for others by inhibiting COX-1 and increasing leukotriene production); penicillins and other antibiotics; insect venom (bee, wasp — Hymenoptera venom anaphylaxis); latex; and infections (acute urticaria is triggered by viral illness — rhinovirus, EBV, hepatitis — in many adults and most children with acute urticaria). Atopic dermatitis (eczema) causes and risk factors: loss-of-function mutations in the filaggrin gene (FLG — found in 30% of patients with atopic dermatitis and responsible for impaired skin barrier function, allowing transcutaneous allergen sensitisation — the primary genetic risk factor for the atopic march); microbiome dysbiosis (Staphylococcus aureus colonises more than 90% of atopic dermatitis skin lesions and drives Th2 inflammation through superantigen toxin production); Th2 cytokine overactivation (IL-4, IL-13, IL-31 — causing itch, IgE class-switching, and further barrier disruption); family history of atopy (if both parents have atopy, child has 70% risk); urban environment, early antibiotic exposure, and reduced microbial diversity (hygiene hypothesis).

Allergic contact dermatitis (ACD) symptoms: an eczematous reaction appearing at the site of allergen contact 24-96 hours after exposure in a previously sensitised individual; the morphology varies with acuity — acute ACD shows erythema, oedema, vesicles (small fluid-filled blisters), bullae, weeping, and crusting; subacute and chronic ACD shows scaling, fissuring, and lichenification (skin thickening from repeated scratching); the pattern and distribution of the rash precisely reflects the shape and location of the contactant (e.g., nickel ACD on earlobes from earrings; the outline of a watch strap on the wrist; nail varnish ACD on the eyelids from transfer by the fingers — not at the application site); intense pruritus is universal; secondary bacterial infection can complicate any ACD with weeping or excoriation. Urticaria (hives) symptoms: transient, well-demarcated, raised, erythematous wheals (plaques) with central pallor and peripheral erythematous flare — classic appearance due to localised mast cell degranulation with histamine release causing vasodilation and plasma extravasation into the dermis; individual wheals last less than 24 hours and resolve without trace (if a lesion persists in the same location beyond 24 hours, urticarial vasculitis should be considered); intense pruritus; lesions migrate and shift location over hours; acute urticaria (below 6 weeks) vs. chronic spontaneous urticaria (above 6 weeks — predominantly autoimmune in 40-50% of cases from anti-FcεRI autoantibodies). Angioedema: deeper swelling in the dermis and subcutaneous tissues rather than the superficial skin — characteristically affecting the lips, tongue, periorbital tissues, and genitalia; less intensely pruritic than urticaria (more painful and tense); involvement of the larynx and pharynx (laryngeal angioedema) causes stridor and voice change and represents a life-threatening airway emergency requiring immediate adrenaline. Atopic dermatitis symptoms: a chronic, intensely pruritic, relapsing-remitting eczema — described as 'the itch that rashes' (pruritus is the primary symptom driving scratching, which then triggers the visible rash); flexural distribution in adults and older children (antecubital and popliteal fossae, wrist flexures, neck, and periorbital); extensor distribution and facial involvement in infants; dry, scaly, lichenified skin (from chronic scratching and rubbing); Dennie-Morgan lines (extra fold of skin below the lower eyelids — associated with atopic dermatitis); and perioral pallor.

Allergic contact dermatitis diagnosis — patch testing (epicutaneous testing): the gold standard investigation for identifying the causative allergen in ACD; thin-film patches impregnated with a panel of standardised allergens (the European Baseline Series contains 30+ allergens, expanded with occupational or speciality series as clinically indicated) are applied to the upper back skin under occlusion for 48 hours, then removed and read at 48 hours (immediate reactions) and 96 hours (late or delayed reactions, which are the clinically significant Type IV responses); a positive reading (redness, induration, and vesiculation at the specific allergen patch site, not at the tape adhesive) with a clinically relevant history of ACD to that allergen confirms sensitisation; patch testing requires the patient to be off systemic immunosuppressants and topical steroids in the test area. Urticaria and angioedema diagnosis: urticaria is primarily a clinical diagnosis based on typical transient whealing lesions with pruritus, no single lesion lasting more than 24 hours; for acute urticaria — identify the likely trigger from history; for chronic spontaneous urticaria (above 6 weeks) — investigate: full blood count (FBC — eosinophilia, anaemia), C-reactive protein (CRP — elevated in urticarial vasculitis), thyroid antibodies (anti-TPO and anti-thyroglobulin — Hashimoto's thyroiditis is a trigger in 5-10% of chronic urticaria); antinuclear antibody (ANA) for connective tissue disease; Helicobacter pylori testing (treat if positive — H. pylori eradication can resolve chronic urticaria in some patients); autologous serum skin test or basophil activation test for autoimmune urticaria; and allergen-specific IgE testing (ImmunoCAP) if a food or drug trigger is suspected. Atopic dermatitis diagnosis: clinical diagnosis using validated criteria — the Hanifin-Rajka major and minor criteria (major: pruritus, typical morphology and distribution, chronic relapsing course, personal or family history of atopy); or UK Working Party criteria (simpler, validated for epidemiological research). Supporting investigations: total serum IgE (commonly elevated in moderate-severe atopic dermatitis but non-specific); allergen-specific IgE (ImmunoCAP/RAST) for sensitisation to food allergens (egg, milk, peanut, wheat) or aeroallergens (house dust mite, animal dander, grass pollen — important in identifying triggers for exacerbations); skin prick test (SPT) as an alternative to specific IgE with similar sensitivity; blood eosinophil count (elevated in moderate-severe atopic dermatitis as a marker of Type 2 inflammation, also used to guide biologic therapy selection). Skin biopsy: rarely required but shows spongiotic dermatitis (intercellular oedema) in eczema — useful when the diagnosis is uncertain and conditions such as mycosis fungoides (cutaneous T-cell lymphoma) or psoriasis need excluding.

Allergen avoidance — most important intervention for all types. ACD: topical corticosteroids (mild: hydrocortisone 1%; moderate: betamethasone 0.1%; strong: clobetasol 0.05%); oral antihistamines for pruritus; short-course systemic steroids for severe ACD. Atopic dermatitis: emollients as cornerstone therapy; topical TCS and calcineurin inhibitors; dupilumab (IL-4/13 inhibitor) or tralokinumab for moderate-severe AD; JAK inhibitors (upadacitinib). Urticaria: non-sedating antihistamines; omalizumab (anti-IgE) for refractory chronic urticaria. Anaphylaxis: epinephrine 0.3-0.5 mg IM immediately. Regular monitoring of treatment response, early detection of side effects, and ongoing assessment of disease progression are essential components of optimising patient outcomes over the long term. Treatment plans should be proactively reviewed and appropriately adjusted based on clinical response, patient-reported tolerability, changing patient circumstances, and continuously evolving evidence-based clinical guidelines. Meaningful shared decision-making between patients and their healthcare team, incorporating patient values and treatment preferences, consistently improves both treatment adherence and long-term outcomes.

Anaphylaxis — life-threatening systemic reaction requiring immediate epinephrine. Bacterial superinfection (Staphylococcus aureus colonizes >90% of atopic dermatitis lesions). Lichenification from chronic scratching. Sleep disturbance, depression, and anxiety. Atopic march: atopic dermatitis → food allergy → allergic rhinitis → asthma — progression in sensitized individuals. Long-term specialist follow-up and structured regular review are essential to detect and appropriately manage complications at the earliest possible stage, minimising long-term disability, preserving organ function, and improving the overall prognosis. Patient education about the early warning signs of complications and clear guidance on when to seek urgent medical attention empowers timely help-seeking behaviour and reduces preventable serious adverse outcomes. Psychological impact — including depression, anxiety, and reduced quality of life — should be proactively assessed and addressed as part of comprehensive complication management.

Identify and consistently avoid confirmed allergens (patch test results). Fragrance-free, hypoallergenic skincare products. Regular emollient use (500g/week for atopic dermatitis) maintains skin barrier. Protective gloves for ACD patients. Allergen immunotherapy (AIT) for selected IgE-mediated allergies. Carry epinephrine auto-injector (EpiPen) if at risk of anaphylaxis. Allergy action plan for schools/workplaces. Sustained lifestyle modifications — maintaining a healthy body weight through balanced diet and regular physical activity, avoiding tobacco smoking, limiting alcohol intake, and managing chronic conditions such as hypertension and diabetes — are foundational strategies for reducing the risk of this condition and its complications. Regular health screening in at-risk populations, rigorous adherence to prescribed preventive medications, and proactive monitoring of established risk factors are equally critical and complementary components of a comprehensive and effective long-term prevention strategy.

Call 999 (emergency services) immediately for signs of anaphylaxis: throat tightness or hoarse voice, difficulty breathing or swallowing, rapid spreading hives combined with dizziness or collapse, pale or bluish skin, and rapid pulse. Administer epinephrine auto-injector (EpiPen) immediately if available — do not wait to see if symptoms improve. Go to A&E or see a doctor urgently for: hives (urticaria) with angioedema (swelling of lips, tongue, eyelids, or throat) even without anaphylaxis; widespread severe skin reactions associated with a new medication (possible Stevens-Johnson syndrome — a rare, life-threatening drug reaction causing painful blistering rash with fever, mouth sores, and eye involvement — always stop the causative drug and seek emergency care); and any skin rash with fever, joint pain, or systemic symptoms requiring exclusion of systemic causes. See your GP or dermatologist for: eczema or contact dermatitis that is not controlled with standard emollients and mild topical steroids — referral for patch testing to identify allergens, or biologics (dupilumab) for moderate-severe atopic dermatitis; chronic urticaria (hives lasting more than 6 weeks) requiring allergy workup and specialist management; and recurrent skin allergic reactions that impair daily life.