Nonanoic acid irritation - a positive control at routine patch testing?

Area of Science:

• Dermatology
• Immunology
• Allergy Testing

Background:

• False negative patch tests can result from procedural errors or impaired immune responses.
• The eliciting (efferent) phase of the immune response is crucial for accurate patch testing.
• A reliable positive control is needed to assess the integrity of this immune phase.

Purpose of the Study:

• To evaluate the efficacy of nonanoic acid as a positive control in patch testing.
• To define the eliciting phase of the immune response in healthy volunteers and dermatitis patients.
• To identify patients with potential defects in their immune response.

Main Methods:

• Dose-response curves were established using various concentrations of nonanoic acid (5%, 10%, 20%, 39.9%) in 1-propanol.
• The irritant was applied to 116 healthy volunteers and 75 dermatitis patients.
• Skin reactions, including erythema and pigmentation, were assessed at 48 and 96 hours.

Main Results:

• Twenty percent nonanoic acid induced skin reactions in 90.1%–93.9% of subjects.
• Observed reactions primarily included erythema at 48 hours and pigmentation at 96 hours.
• This concentration effectively served as a positive control, eliciting responses in most participants.

Conclusions:

• Nonanoic acid, particularly at 20% concentration, is an effective primary irritant for use as a positive control in patch testing.
• Patients who do not react to this primary irritant warrant further investigation for potential immune response defects.
• This method aids in differentiating procedural errors from genuine immune system issues in false negative patch tests.