Irritant patch testing with sodium lauryl sulphate: interrelation between concentration and exposure time.

BACKGROUND

It is well known that the degree of skin reaction to an irritant depends on its concentration and exposure time.

OBJECTIVES

To determine the interrelationship between the concentration of sodium lauryl sulphate (SLS) and exposure time in both weak (subclinical) and severe reactions.

METHODS

Patch testing with SLS was performed at different concentrations (0.125%, 0.25%, 0.5%, 1.0% and 2.0%) and with different exposure times (3, 6, 12, 24 and 48 h). Evaluation was conducted by measurement of transepidermal water loss and by laser-Doppler flowmetry both 30 min and 24 h after patch removal.

RESULTS

We found more reliable and constant skin reactions 24 h after patch removal, and a higher correlation between SLS concentration and skin reaction.

CONCLUSIONS

We conclude that the concentration of SLS influences the test outcome to a larger degree than the exposure time. We present formulae by which the outcome of SLS patch testing at various SLS concentrations ranging from 0.125% to 2% and any exposure time between 3 and 24 h can be estimated.