Patient Information
Allergic reactions occur when the body's immune system overreacts to a substance it incorrectly identifies as a threat. These substances — known as allergens — can include certain foods, insect venom, pollen, medications, animal dander, latex, and many more. The severity of the reaction varies widely: from mild localised skin irritation to severe systemic anaphylaxis. Prompt identification of the trigger and appropriate treatment are key to patient safety and long-term management.
Common Triggers
Food Allergens
Food allergies are among the most common and can range from mild GI discomfort to severe anaphylaxis. Reactions typically begin within minutes to two hours of ingestion.
Insect Stings & Bites
Venom from stinging insects introduces foreign proteins that trigger immune responses. Most reactions are local, but sensitive individuals may develop severe systemic reactions.
Medications
Drug allergies can present as mild rashes or — in rare cases — as life-threatening anaphylaxis. Any new rash appearing after starting a medication should be evaluated promptly.
Environmental Allergens
Airborne particles and environmental substances cause a wide range of allergic symptoms from seasonal hay fever to year-round rhinitis and skin reactions.
Contact Allergens
Direct skin contact with certain substances produces localised allergic contact dermatitis — redness, itching, and blistering at the point of contact.
Physical Triggers
In some individuals, physical stimuli can provoke allergic-type responses. These are less common but can significantly impact quality of life.
Signs & Symptoms
Rash or hives
Raised, red, itchy welts or a more widespread skin rash — one of the most common presentations of a mild allergic reaction
Swelling
Especially around the eyes, lips, face, or throat (angioedema) — throat swelling is a warning sign of anaphylaxis and requires immediate emergency care
Itchy, watery eyes or nose
Allergic rhinitis and conjunctivitis — very common with environmental and seasonal allergens such as pollen and animal dander
Sneezing and nasal congestion
Triggered by airborne allergens entering the nasal passages — may be seasonal or perennial depending on the trigger
Wheezing or difficulty breathing
Bronchospasm or throat swelling restricting airflow — a sign of a severe or potentially life-threatening reaction requiring emergency treatment immediately
Dizziness, rapid heartbeat, or fainting
Signs of anaphylactic shock — the immune response affects the cardiovascular system, causing a dangerous drop in blood pressure
Mild
Localised Reaction
- Hives or skin rash
- Itchy eyes or nose
- Sneezing
- Minor swelling at sting site
Moderate
Spreading Reaction
- Widespread hives
- Facial swelling
- Vomiting or abdominal cramps
- Tightness in the chest
Severe — Call 911
Anaphylaxis
- Throat closing or swelling
- Difficulty breathing
- Rapid or weak pulse
- Loss of consciousness
Diagnostic Labs
Skin Prick Test
Specific Allergen Identification
Small amounts of suspected allergens are placed on the forearm or back and lightly pricked into the skin. A raised, red weal at a test site within 15–20 minutes confirms a specific allergic sensitisation. This is the gold standard for identifying environmental, food, and venom allergies and directly guides avoidance advice and allergy immunotherapy planning.
Blood Tests — Specific IgE (RAST/ImmunoCAP)
Allergy Testing
A blood sample is taken and tested for elevated levels of allergen-specific immunoglobulin E (IgE) antibodies — the immune proteins responsible for triggering allergic reactions. This method is particularly useful when skin testing is not feasible (e.g. severe eczema, use of antihistamines) and can quantify the degree of sensitisation to specific allergens including foods, pollens, and venoms.
Treatment Options
First-Line · All Mild Reactions
Antihistamines
Oral or topical antihistamines block the histamine receptors responsible for itching, redness, swelling, and runny nose. First-line treatment for mild to moderate allergic reactions including hives, food reactions, and insect sting responses.
Moderate Rashes · Inflammation
Corticosteroids
Topical corticosteroid creams reduce localised skin inflammation from contact reactions and eczema flares. Oral steroids are prescribed for more widespread or severe allergic skin reactions where antihistamines alone are insufficient.
Emergency · Anaphylaxis Only
Epinephrine (Adrenaline)
The only definitive treatment for anaphylaxis. Epinephrine reverses airway swelling, restores blood pressure, and counteracts the systemic effects of a severe allergic reaction. Must be administered immediately — always followed by emergency hospital assessment.
Long-Term · Prevention
Allergen Avoidance & Management
For known allergens, a structured avoidance plan is the most effective long-term strategy. This includes reading food labels, wearing medical alert identification, and working with our Allergy Medicine team on desensitisation programmes where appropriate.
Follow-Up Guidance
Return or follow up after any severe allergic reaction
Even if emergency treatment was successful, any patient who has experienced anaphylaxis or a severe allergic reaction should follow up with a physician. This allows for allergen identification testing, prescription of emergency medication, and a personalised management plan to prevent future reactions.
Allergy Medicine referral for ongoing or complex allergies
Patients with recurrent or difficult-to-manage allergies are referred to our in-house Allergy Medicine team for specialist evaluation, comprehensive allergen testing, and consideration of allergy immunotherapy — a long-term desensitisation treatment that can reduce reaction severity and frequency.
Specialist Allergy Medicine — In-House
Comprehensive allergy care available at Foggy Bottom Clinic
Beyond urgent allergic reactions, our Allergy Medicine team manages the full spectrum of allergic disease — from hay fever to asthma, food allergies, and anaphylaxis risk management. All under one roof.
Allergic Rhinitis
Asthma
Food Allergies
Anaphylaxis
Drug Allergies
Urticaria (Hives)