• behind-the-knee;
  • contact dermatitis;
  • erythema;
  • non-invasive measuring method;
  • patch test;
  • polarized light;
  • skin irritation;
  • subclinical

Background/purpose:  Polarized light has been used as an aid in visualizing various skin conditions, including acne vulgaris, rosacea, photoageing, lentigo simplex, and basal cell carcinoma. The use of parallel-polarized and cross-polarized light was evaluated in mild irritant reactions to determine, if this increases the ability to detect very early stages or low levels of irritation.

Methods:  Low concentrations of sodium lauryl sulfate (0.01% and 0.1%) were patched on human volunteers for 2, 6, and 24 hr, daily for 2–3 days in a modification of the standard patch test. Feminine protection products were evaluated in the behind-the-knee (BTK) test. Erythema reactions were scored by unaided visual assessment and using a polarized light visualization system.

Results:  In the 24-hr patch test, mean erythema assessed with polarized light was consistent with results of unaided visual scoring. Under milder conditions (2- and 6-hr patches), and in the BTK, significant differences from pretreatment levels of erythema were apparent earlier in the series of treatments compared with unaided scoring. In addition, subsurface scoring demonstrated that changes were still present under the skin surface even after unaided visual scoring indicated recovery.

Conclusion:  Low (subclinical) levels of irritation can be detected using enhanced visual scoring, indicating this non-invasive method has the potential to increase the sensitivity of our clinical studies.