Increased vascular permeability
Formation of wheal and surrounding erythema
The wheal size reflects the degree of allergic sensitization but does not always correlate with clinical severity.
Common Allergens Tested
A skin prick panel may include:
Environmental Allergens
House dust mites
Grass pollen
Tree pollen
Weed pollen
Mold spores
Animal dander
Cockroach allergens
Food Allergens
Milk
Egg
Peanut
Soy
Wheat
Fish
Shellfish
Tree nuts
Occupational Allergens
Latex
Flour
Animal proteins
Insect Allergens
Bee venom
Wasp venom
Fire ant venom
Indications
Healthcare providers recommend skin prick testing for patients with:
Seasonal allergies
Persistent rhinitis
Asthma
Atopic dermatitis
Food allergy
Recurrent allergic reactions
Insect sting allergy
Drug allergy evaluation (selected cases)
Contraindications
Skin testing may not be suitable for:
Severe eczema affecting testing areas
Recent anaphylaxis
Uncontrolled asthma
Patients taking antihistamines that cannot be stopped
Individuals with certain skin disorders
Patients with a history of severe reactions to testing
Patient Preparation
Before testing, patients should:
Stop antihistamines several days beforehand (as instructed by their clinician)
Inform the healthcare provider about all medications
Avoid applying creams to the testing area
Wear loose clothing
Report any recent allergic reactions or illnesses
Equipment Required
The procedure requires:
Sterile lancets
Allergen extracts
Positive control (histamine)
Negative control (saline or glycerin)
Alcohol swabs
Marker pen
Measuring ruler
Emergency medications
Procedure
Step 1
The patient’s identity is confirmed.
Step 2
The testing area is cleaned.
Step 3
The skin is marked with numbered locations.
Step 4
Drops of allergens are placed according to the numbering.
Step 5
Each drop is gently pricked.
Step 6
Excess allergen is removed.
Step 7
The patient waits approximately 15–20 minutes.
Step 8
The wheal sizes are measured.
Step 9
Results are recorded.
Interpretation
The image shows multiple raised wheals of different sizes. In practice:
No wheal: Negative
Small wheal: Mild sensitivity
Medium wheal: Moderate sensitivity
Large wheal: Strong sensitivity
The histamine control should produce a positive reaction, while the negative control should not.
Reading the Results
Measurements usually include:
Wheal diameter
Flare diameter
Presence of redness
Comparison with controls
A wheal generally measuring 3 mm or more than the negative control is often considered positive, though interpretation depends on the clinical context and testing protocol.
Advantages
Benefits include:
Rapid results
High sensitivity
Relatively inexpensive
Minimal discomfort
Can test many allergens at once
Helps guide avoidance strategies and treatment
Limitations
Limitations include:
False positives
False negatives
Medication interference
Requires intact skin
Must be interpreted alongside symptoms
Positive results indicate sensitization, not necessarily clinical allergy
Risks
Most reactions are mild.
Possible side effects include:
Itching
Redness
Swelling
Local discomfort
