Private penicillin allergy clinic in London, same-day GP.

Why so many labels are wrong

• A rash during a childhood illness — frequently the virus rather than the antibiotic. This is the single commonest reason.
• Side effects mistaken for allergy — nausea, diarrhoea, thrush and headache are side effects, not allergic reactions.
• A family member's allergy — drug allergy is not meaningfully inherited.
• Genuine allergy that has faded — around 80% of people with a true penicillin allergy lose it after ten years.
• No recollection at all — a label added decades ago that nobody has revisited.

What your history tells us

• What exactly happened — rash, swelling, breathing difficulty, vomiting?
• How soon after the dose — within an hour suggests a true immediate allergy; days later suggests something different.
• How long ago, and how old you were.
• What treatment was needed — nothing, antihistamine, adrenaline, admission?
• Have you had a penicillin since, knowingly or not? Many people have, without incident.
• Photographs, if any exist, are genuinely useful.

Testing

Where the history suggests a low risk, the label can often be removed after assessment, sometimes with a supervised oral challenge. Where the history is less clear, skin testing followed by a challenge is used. Testing is done in a setting equipped to manage a reaction, and is safe when the right people are selected.

Who should not be tested

• anyone who has had a severe blistering or peeling skin reaction, or DRESS
• anyone with organ involvement — liver or kidney — attributed to the drug
• those with unstable asthma or uncontrolled heart disease at the time
• people on medicines that would interfere, such as beta-blockers, until reviewed
• For these groups the label stays, and the value lies in recording exactly what happened so that alternatives are chosen sensibly.