Why you can’t rely on swabs to quantify allergen residues

9 June 2025. By FACTS in Allergen Management

Testing for the presence or absence of allergen residues on surfaces using swabs is well established. However, accurately quantifying allergenic residues on surfaces using swabs is far more complex — and not currently considered scientifically reliable.

Experts caution against quantitative allergen testing of surface swabs. Here are three key reasons why.

SAMPLING VARIABILITY

The process of collecting surface samples is inherently variable. Many factors can affect the amount of allergen residue recovered from a surface, including:

Swab type
Swab absorption capacity
Contact surface characteristics
Allergen residue adsorption to the food contact surface
Swabbing technique
Size of the area swabbed
Presence of cleaning and sanitation agents on surfaces

VALIDATION/VERIFICATION CHALLENGES

Most quantitative allergen tests are developed and validated for food matrices. This ensures that the test is appropriate to the food sample being analysed. In the case of surfaces, there is currently no consensus on how to validate and verify a quantitative test – as a result of the challenges outlined above, amongst others.

UNIT MISMATCH

For food samples, quantitative allergen testing measures the milligrams of allergenic protein per kilogram of sample (mg/kg), based on a known test portion, such as one gram. In the case of surface swabs, the swab is not actually the sample – but rather the surface that is being swabbed. Therefore, a more appropriate unit would be milligrams of allergenic protein per square centimetre of surface swabbed (mg/cm²). Yet, surface area is rarely recorded or communicated with laboratories, and allergen sampling points are typically areas that are difficult to measure.

So, what does this mean for allergen testing?

Given these variables, it is not currently scientifically sound to accurately quantify allergen residues on swab samples.

Surface swabbing remains a valuable monitoring tool in an allergen management programme — but only for verifying the presence or absence of allergens on surfaces, not measuring the amount of allergen residues on a surface.

For more information on allergen testing and management, please visit our Allergen Management page or contact our team directly.

Other articles, resources and videos you may be interested in:
The building blocks of a recall-proof allergen control plan
Stepping through allergen cleaning