A study of skin responses to follow-up, rechallenge and combined effects of irritants using non-invasive measurements

Irritant contact dermatitis is a common clinical problem. Primary irritation can be easily recognized, but cumulative irritation by daily exposure is hard to be diagnosed and the condition may fail to be clear even away from work. The mechanism of irritant dermatitis produced by repeated or combined exposure to clinical or subclinical doses of irritants is still poorly understood. In order to find out whether the subclinical doses of irritants affect each other by repeated or combined exposure according to their concentrations, non-invasive measurements, transepidermal water loss and laser Doppler flowmetry were used. Sodium lauryl sulfate, sodium hydroxide and benzalkonium chloride were serially diluted and patch-tested with large Finn chambers on Scanpor tape on the back of normal human volunteers and responses were followed up for 7 days. Twice repeated exposure with subclinical doses of irritants at 1 day intervals were also performed. Repeated daily applications for 5 days with subclinical doses of single or premixed irritants were performed to know the combined irritating effect. The irritant response was well correlated to the concentration of the irritants. However, increased response was not observed when subclinical doses were rechallenged on the previously patch tested sites. Twice-repeated exposure of subclinical doses of irritants increased skin irritancy when measured by transepidermal water loss and laser Doppler flowmetry. Some correlation and some discrepancies were observed between different evaluation methods in combined and repeated application tests with irritants of subclinical doses. Responses of skin irritancy induced by subclinical doses showed somewhat different pattern from that given strong irritants. So, when evaluating the patients suspicious of irritant dermatitis, patch testing with the possible combination of the irritants or repeated test may be helpful to verify their effect on the skin even at a weak concentration.