Skin prick testing: a parent's guide

What is skin prick testing?

Skin prick testing (SPT) is a quick, safe, and well-established way to identify whether a child's immune system has produced IgE antibodies against specific allergens. A small drop of allergen extract is placed on the forearm and a lancet creates a tiny scratch beneath the drop. After 10-15 minutes, any raised weal at the site indicates sensitisation to that allergen.

SPT is performed under Dr Sood's direct supervision, with emergency anaphylaxis medication immediately available.

Preparing for the test

The most important step is stopping antihistamines in advance: they suppress the skin response and will give a false negative result. Stop antihistamine 72 hours before your appointment.

Cetirizine, loratadine, fexofenadine, Chlorphenamine (Piriton), Hydroxyzine, cough syrups etc.

Do not apply moisturiser or steroid cream to the test area on the day.

Most other medications (including asthma inhalers) can be continued as normal.

What happens on the day

Testing takes around 20–30 minutes in total. The forearm is cleaned and small drops of allergen extracts are placed in a row. A lancet is used to make a tiny scratch beneath each drop. Most children find this causes no more than a mild tickle. After 10-15 minutes, the results are read. Any weal measuring 3mm or more is considered positive.

Understanding the results

A positive result means sensitisation: the immune system has produced IgE antibodies against that allergen. It does not automatically confirm clinical allergy. Many sensitised children have no symptoms on eating the relevant food.

Dr Sood interprets results alongside the full clinical history. A positive peanut test in a child who eats peanut butter regularly without symptoms means something very different from a positive result in a child who has reacted severely to trace amounts.

What happens next

Based on the results and clinical history, Dr Sood will recommend one of several approaches: dietary avoidance with an emergency action plan, a supervised food challenge to clarify allergy status, or allergy testing for additional allergens. All recommendations are explained clearly at the appointment and summarised in a written report.