Urticaria and allergic reactions
Look at the airway first. Skin only? A non-sedating antihistamine. Any airway, breathing or circulation problem? IM adrenaline.
A 30-year-old woman has itchy raised wheals all over her body for 3 hours after eating prawns at a wedding. No wheeze, no throat tightness, no dizziness. BP 124/80, SpO₂ 99%.
A 58-year-old man on lisinopril for 2 years has a swollen tongue and lower lip that started this morning. No rash or itch. His voice sounds thick.
Which one is the airway emergency, and why won't antihistamines fix it?
- Exclude anaphylaxis firstAirway swelling, wheeze, low BP, collapse, gut symptoms after a trigger: IM adrenaline.
- Tongue or lip swelling without hives on an ACE inhibitorBradykinin angioedema: airway risk, senior and anaesthetist early.
- Hives aloneNon-sedating antihistamine.
- Find the triggerFood, drug, infection, insect, physical, often unknown.
- Short oral steroidOnly for severe or persistent acute urticaria.
- Chronic urticaria (6 weeks or more)Daily antihistamine, up to 4 times the standard dose.
- AdviceAvoid known triggers. NSAIDs and opioids can worsen urticaria.
- Throat tightness, voice change, stridor, drooling
- Wheeze, low BP or collapse
- Tongue swelling
- Swelling worsening quickly
- Hives with fever and joint pains
- Anaphylaxis
- ACE inhibitor angioedema
- Hereditary angioedema (no hives, family history, abdominal attacks)
- Urticarial vasculitis (lesions over 24 hours, bruising)
- Serum sickness
| Cetirizine | 10 mg once daily (chronic: up to 4 times this dose under guidance) |
| Fexofenadine | 180 mg once daily |
| Prednisolone | 40 mg daily for up to 5 days in severe acute urticaria |
| Acute urticaria | Under 6 weeks, usually viral, food or drug |
| Chronic urticaria | 6 weeks or more, usually no external trigger |
| IM adrenaline | 0.5 mg (adult) for anaphylaxis |
Check every dose against a current drug reference and your hospital protocol.
On this page
Hives, angioedema or anaphylaxis?
- Antihistamine
- avoid trigger
- review
- Antihistamine
- observe
- look for trigger
Anaphylaxis: IM adrenaline 0.5 mg, A–E
- Bradykinin angioedema
- antihistamines and adrenaline may not work
- airway team
Two kinds of swelling
| Feature | Histamine (mast cell) | Bradykinin |
|---|---|---|
| Hives and itch | Usually present | Absent |
| Causes | Food, drugs, insects, infection, idiopathic | ACE inhibitors, hereditary or acquired C1 inhibitor deficiency |
| Speed | Minutes to hours | Hours, lasts 2–5 days |
| Response to adrenaline and antihistamines | Good | Poor |
| Risk | Anaphylaxis | Airway obstruction |
ACE inhibitor angioedema can start years after the drug was started. Stop the ACE inhibitor for life. ARBs are usually avoided or used with caution.
History
- Timing: when did it start, how long does each wheal last (under 24 hours in ordinary urticaria)?
- Trigger: food, new drug (antibiotics, NSAIDs, contrast), insect sting, infection, exercise, heat, cold, pressure.
- Swelling of lips, tongue, throat; breathing, voice, dizziness, abdominal pain, vomiting.
- ACE inhibitors (lisinopril, enalapril, ramipril, captopril).
- Previous episodes, family history of swelling.
Acute or chronic?
| Type | Duration | Usual cause | Management |
|---|---|---|---|
| Acute urticaria | Under 6 weeks | Viral infection, food, drugs | Antihistamine, avoid trigger |
| Chronic spontaneous urticaria | 6 weeks or more | Usually none found (autoimmune) | Daily antihistamine, up-dosing, specialist if not controlled |
| Physical urticaria | Episodes with a trigger | Pressure, cold, heat, exercise, scratching (dermographism) | Avoid trigger, antihistamine |
Investigations
- Acute urticaria: usually none.
- Chronic urticaria: CBC, CRP or ESR, thyroid function if symptoms; avoid long panels of allergy tests.
- Angioedema without hives: C4 (and C1 inhibitor if low) for hereditary angioedema.
- Lesions lasting over 24 hours, bruising, fever, joint pains: consider urticarial vasculitis (biopsy).
Treatment
Common mistakes
- Treating anaphylaxis with antihistamines and steroids only.
- Missing ACE inhibitor angioedema because the patient has taken the drug for years.
- Giving long courses of oral steroids for chronic urticaria.
- Ordering big allergy panels for chronic urticaria.
- Letting the patient continue the culprit drug.
Frequently asked questions
What is the best antihistamine for urticaria?
A non-sedating antihistamine such as cetirizine or fexofenadine once daily. In chronic urticaria the dose can be increased up to four times under guidance.
What causes angioedema without hives?
ACE inhibitors and hereditary or acquired C1 inhibitor deficiency (bradykinin-mediated). These respond poorly to antihistamines and adrenaline; involve the airway team early.
How long does urticaria last?
Acute urticaria settles within 6 weeks, usually much sooner. Chronic urticaria lasts 6 weeks or more and often for months.
When is urticaria an emergency?
When there is throat or tongue swelling, breathing difficulty, wheeze, low BP or collapse: treat as anaphylaxis.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A woman has itchy wheals after eating prawns but no airway, breathing or circulation problems. What is the treatment?
Answer: Cetirizine. Cetirizine or fexofenadine for acute urticaria.
- Antibiotics: No.
- Observation only: Treat itch.
- IV hydrocortisone: Not needed.
- IM adrenaline: Not needed without anaphylaxis.
2. A patient on lisinopril has tongue swelling without hives. Which statement is correct?
Answer: It may resist adrenaline. ACE inhibitor angioedema is bradykinin-mediated; involve the airway team early.
- Give antibiotics: No.
- It is a food allergy: Bradykinin-mediated.
- Continue lisinopril: Must stop.
- It is always mild: Can obstruct the airway.
3. How is chronic urticaria defined?
Answer: Hives on most days for 6 weeks or more. Chronic urticaria lasts 6 weeks or more; daily antihistamine is the main treatment.
- Hives for 3 days: Acute.
- Hives after one food: Acute.
- Hives with fever: Not the definition.
- Hives lasting over 24 hours each: Suggests vasculitis.
4. A 22-year-old has recurrent swelling of the lips and abdomen without urticaria or itch since adolescence. Antihistamines and adrenaline don’t help. Low C4 is found. What is deficient?
Answer: C1 esterase inhibitor. Hereditary angioedema (autosomal dominant, C1-INH deficiency or dysfunction) causes bradykinin-mediated non-itchy swelling of skin, gut (abdominal pain) and larynx (life-threatening), without urticaria. Triggers: trauma, dental work, oestrogens, ACE inhibitors. C4 is low between attacks. Acute attacks: C1-INH concentrate, icatibant (bradykinin B2 antagonist); FFP if unavailable. Antihistamines, steroids and adrenaline are ineffective.
- IgE: IgE-mediated angioedema comes with urticaria and responds to adrenaline.
- Complement C3: C3 is not the deficient factor in hereditary angioedema.
- Histamine N-methyltransferase: This enzyme is not linked to bradykinin angioedema.
5. A 55-year-old who started lisinopril 2 months ago presents with swelling of the lips and tongue without urticaria or itching; airway is patent. What is the most important step?
Answer: Stop the ACE inhibitor permanently. ACE-inhibitor angioedema: bradykinin-mediated (reduced breakdown) — lips, tongue, face, airway; no urticaria/pruritus; can occur months–years after starting; commoner in people of African ancestry, smokers. Responds poorly to antihistamines/steroids/adrenaline (may still be given if airway threatened); icatibant or FFP in severe cases; airway management. Stop ACE inhibitor permanently; ARBs carry a small risk (use cautiously); avoid sacubitril–valsartan. Histamine angioedema: with urticaria, itch — antihistamines.
- Switch to another ACE inhibitor: ACE inhibitor angioedema is a class effect.
- Continue and add antihistamine: Continuing risks recurrence.
- Give penicillin: This is not infective.
6. To prove medical negligence, which elements must be shown?
Answer: Duty, breach, harm and causation. Negligence requires: the doctor owed a duty of care, fell below the accepted standard (often judged against what a responsible body of doctors would do), the patient suffered harm, and the breach caused that harm. A known complication without a breach is not negligence.
- Breach and harm only: Harm must also be caused by the breach.
- Duty and breach only: Without resulting harm there is no negligence claim.
- Harm and causation only: A breach of a duty of care must also be shown.
- Duty, harm and intent to harm: Negligence does not require intent.
7. A child with hypocalcaemic tetany, recurrent viral and fungal infections and a cardiac outflow defect most likely has:
Answer: DiGeorge syndrome (22q11 deletion). DiGeorge syndrome: failure of the 3rd and 4th pharyngeal pouches. CATCH-22: Cardiac defects (truncus arteriosus, tetralogy), Abnormal face, Thymic aplasia (T cell deficiency), Cleft palate, Hypocalcaemia (absent parathyroids), 22q11 deletion (FISH).
- Bruton agammaglobulinaemia: B cells absent; bacterial infections.
- Chronic granulomatous disease: Phagocyte defect.
- Wiskott–Aldrich syndrome: Eczema, thrombocytopenia, infections.
- Selective IgA deficiency: Often mild; anaphylaxis to blood products.
References and dose sources
- NICE CKS — Urticaria
- Resuscitation Council UK — Anaphylaxis (2021)
- Cetirizine dosing: Drugs.com: Cetirizine dosage (see also our cetirizine dose page)
- Prednisolone dosing: Drugs.com: Prednisolone dosage (see also our prednisolone dose page)
- Chlorphenamine (chlorpheniramine) dosing: Drugs.com: Chlorpheniramine dosage (see also our chlorphenamine (chlorpheniramine) dose page)
- Adrenaline (epinephrine) dosing: Drugs.com: Epinephrine dosage (see also our adrenaline (epinephrine) dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.