01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Define the exact stimulus rather than labelling all exercise-related wheals as heat allergy. Ask about scratching, straps, carrying, delayed pressure, vibration, cold air or water, sweating, emotional heat, sunlight, water itself and contact substances. A diary should include latency and lesion duration because delayed-pressure disease appears long after the initiating load.
Provocation confirms reproducibility and can estimate threshold, but testing must be matched to risk. A small local cold device is not equivalent to whole-body immersion; negative local testing does not guarantee swimming safety. Exercise or solar testing belongs in an appropriately supervised setting when systemic symptoms have occurred.
Clinical decisions in Inducible urticarias depend on trajectory and consequence. Re-examine evolving skin, repeat focused systemic assessment when the patient changes, and reconcile every result with morphology and timing; a normal early test cannot neutralise worsening pain, mucosal injury or organ dysfunction.
Key points
- A consistent stimulus-to-wheal relationship distinguishes inducible urticaria; document delay, threshold, duration and whether symptoms extend beyond exposed skin.
- Symptomatic dermographism causes itchy linear wheals after stroking, whereas simple dermographism without symptoms does not require treatment.
- Cholinergic urticaria produces small itchy wheals with heat, emotion or exercise; systemic exertional symptoms require evaluation for exercise-induced anaphylaxis.
- Cold urticaria carries a particular risk during swimming or whole-body cooling, so unsupervised immersion challenge is unsafe.
- Provocation tests should reproduce the suspected trigger in a controlled graded way with emergency readiness when systemic reactions are plausible.
- Management combines realistic trigger modification, a regular second-generation H1 antihistamine and a written emergency plan for higher-risk phenotypes.
- Inducible urticarias must be assessed by lesion duration, onset, distribution, symptoms, mucosal findings, systemic physiology and the full medicine timeline rather than by colour alone.
- For Inducible urticarias, document the working diagnosis, excluded emergencies, uncertain culprit or trigger, treatment response and the exact safety-net given.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Mechanical stimulation
Stroking, scratching, vibration or sustained pressure can trigger mast-cell mediator release at exposed sites, with timing varying from minutes to several hours.
Temperature and sweat triggers
Cold contact, rising core temperature, exercise or local heat provoke distinct phenotypes whose systemic risk depends on dose and exposed surface area.
Light, water and contact triggers
Solar, aquagenic and contact urticarias are uncommon but reproducible; the causal wavelength, water-independent friction or specific contact substance requires careful separation.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Stimulus-threshold activation
A physical input exceeds an individual threshold and activates cutaneous mast cells, producing a wheal in the geometry of the exposure.
- 2Immediate mediator effects
Histamine-driven vascular dilation and permeability cause itch, oedema and erythema or colour change within minutes in dermographism, cold and cholinergic disease.
- 3Delayed-pressure inflammation
Sustained load can produce deep painful swelling several hours later and is easily missed when history focuses only on immediate skin change.
- 4Whole-body dose effect
Swimming, vigorous exertion or widespread exposure recruits enough mediator release to create systemic symptoms beyond the local skin response.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Linear itchy wheals appear within minutes of firm stroking and fade, distinguishing symptomatic disease from asymptomatic skin writing.
Deep tender oedema develops several hours after straps, standing, carrying or tight clothing and may persist much longer than a superficial wheal.
Numerous tiny itchy wheals with surrounding flare follow sweating, heat, emotion or exercise and usually begin on trunk and limbs.
Generalised wheals, dizziness, breathing difficulty or collapse with swimming indicates anaphylaxis risk and requires strict safety planning.
Wheals confined to a light-exposed or substance-contact boundary arise quickly and should fade after the stimulus ends.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Detailed stimulus diaryFirst step - Why
- Establish reproducibility, latency, threshold and cofactors before challenge.
- Interpretation and limitations
- Record medicines, foods, exercise, infection and menstrual or alcohol cofactors; frequent spontaneous wheals can create a false trigger association.
- 02
Standardised dermographism provocation - Why
- Confirm symptomatic whealing after calibrated stroking.
- Interpretation and limitations
- A visible line without itch is common and not sufficient for the clinical diagnosis; antihistamines can suppress the response.
- 03
Controlled cold provocation - Why
- Assess local cold whealing and threshold under supervised conditions.
- Interpretation and limitations
- The method and rewarming response matter; avoid unsupervised ice or immersion challenges when systemic reactions are possible.
- 04
Exercise or passive warming challenge - Why
- Differentiate cholinergic urticaria from exertional anaphylaxis in specialist care.
- Interpretation and limitations
- Monitor for systemic symptoms and cofactors; a negative challenge on one day may not reproduce the patient’s threshold.
- 05
Targeted allergy or phototesting - Why
- Investigate contact or solar urticaria when history identifies a precise exposure.
- Interpretation and limitations
- Select the suspected agent or wavelength rather than broad panels, and maintain resuscitation readiness for immediate reactions.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Chronic spontaneous urticaria
Wheals arising without consistent provocation can coexist with an inducible phenotype and should be measured separately in the history.
Exercise-induced anaphylaxis
Systemic symptoms linked to exertion, sometimes requiring a food or medicine cofactor, exceed ordinary cholinergic whealing and demand specialist evaluation.
Mastocytosis or clonal disease
Recurrent severe flushing, hypotension, sting anaphylaxis or persistently raised baseline tryptase may indicate a mast-cell disorder rather than isolated physical urticaria.
Inflammatory and vascular mimics
Erythromelalgia, autoinflammatory fever syndromes, Raynaud phenomena and contact dermatitis produce different lesion duration and associated symptoms.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Local reproducible symptomsConfirm and reduce the specific exposureFirst stepWheals remain local, physiology is normal and a consistent physical trigger is identifiable.+
- 1Document the stimulus, latency and threshold, then perform a low-risk standardised provocation when confirmation will change behaviour or treatment.
- 2Modify exposure proportionately using protective layers, load breaks, temperature planning or contact substitution instead of prohibiting all activity.
- 3Use a regular non-sedating H1 antihistamine when symptoms persist, measure control and reconsider coexisting spontaneous urticaria.
02Systemic-risk phenotypeCreate an anaphylaxis-safe planCold, exercise or contact exposure has caused throat, breathing, circulatory or widespread gastrointestinal symptoms.+
- 1Avoid the high-dose trigger, especially swimming alone or sudden cold immersion, until specialist assessment defines a safer threshold and cofactors.
- 2Provide an adrenaline auto-injector when indicated, demonstrate use, ensure two in-date devices are carried and give a written emergency plan.
- 3Treat recurrent ABC compromise as anaphylaxis immediately; antihistamines cannot substitute for intramuscular adrenaline.
03Unclear or treatment-resistant patternReassess mechanism with specialist testingReported triggers are inconsistent, multiple phenotypes coexist or licensed-dose treatment does not control daily life.+
- 1EscalationSeparate spontaneous from provoked episodes using timed photographs and a structured diary before escalating medication.
- 2Refer for calibrated threshold testing and specialist-guided antihistamine up-dosing or advanced therapy where disease burden warrants it.
- 3Review occupational and psychological consequences so risk advice remains practical and does not create avoidable disability.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Cetirizine 10 mg tablets
Adults and adolescents aged 12 years and over take 10 mg orally once daily, with renal dose adjustment according to the SmPC.Check somnolence, driving, alcohol, renal function, pregnancy and breastfeeding; specialist-supervised doses above the licence remain off-label and require documented discussion.
Adrenaline auto-injector 300 micrograms
Adults at risk use one 300 microgram intramuscular auto-injector into the outer thigh at anaphylaxis onset and call emergency services; use a second after five minutes if not improving.Device strength must match the individual; train with the exact brand, carry two devices, check expiry, inject through clothing if necessary and never rely on antihistamine first.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Drowning and collapse
Sudden immersion in cold water can provoke widespread mediator release, hypotension or airway symptoms while simultaneously impairing safe swimming.
Occupational disability
Pressure, vibration, heat or contact exposures can restrict work and daily tasks when risk reduction is not tailored to the actual stimulus threshold.
Anxiety and over-avoidance
Unclear triggers may lead to severe activity, bathing or dietary restriction that exceeds physiological risk and worsens quality of life.
Treatment sedation
Reliance on sedating antihistamines around driving, machinery or water activity creates additional preventable harm through impaired alertness and coordination.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Track exposure threshold, wheal frequency, systemic symptoms and restrictions on work, exercise, bathing and swimming for inducible urticaria.
- Recheck auto-injector technique, expiry dates and the patient’s plan for companions or workplaces after any systemic episode.
- Review whether trigger avoidance remains proportionate as control improves and whether spontaneous wheals have emerged independently.
- At every review of Inducible urticarias, record lesion evolution, new mucosal or systemic features, medicine changes, treatment adherence and adverse effects.
- Give a named route for urgent reassessment if breathing, circulation, fever, skin pain, blistering, facial swelling, reduced urine output or other organ symptoms develop during Inducible urticarias.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Latency identifies pressure disease
Swelling that appears at night may reflect a shoulder strap or prolonged standing many hours earlier.
Swimming multiplies exposure
Large cold surface area plus distance from help makes aquatic reactions more dangerous than a local cold-object wheal.
Tiny wheals suggest cholinergic disease
Punctate lesions after sweating are useful, but collapse or airway symptoms move the differential toward anaphylaxis.
Threshold can change
Infection, stress and active spontaneous urticaria may lower the amount of physical stimulus needed to provoke symptoms.
Negative local cold testing is limited
A small challenge cannot certify that whole-body immersion will be safe under different temperature and cofactor conditions.
11Common pitfallsFrequent interpretation and management errors.
- 01
Advising a previous cold-water reactor to test tolerance by swimming alone.
- 02
Diagnosing cholinergic urticaria from exercise alone without asking about food-dependent or medicine cofactors.
- 03
Treating asymptomatic dermographism observed during examination as a disease needing medication.
- 04
Missing delayed-pressure urticaria because lesions were absent immediately after the provoking load.
- 05
Recommending broad avoidance that stops employment or exercise without measuring the actual trigger threshold.