Objective To investigate the impact of synthetic urine (synurine solution) at differentpH values on skin surface.Methods Sixty-four healthy volunteers were enrolled into this study.Based on the results of lactic acid test and questionaires,these subjects were enrolled as sensitive skin group and normalskin group.The 4-,20-,and 24-hour occlusive patch tests were successively performed with synthetic urine at various pH values (2.0,3.5,5.0,6.5,8.0 and 10.0)on the two groups of volunteers.The distilled waterand 0.25%sodium lauryl sulphate (SLS)served as control.The skin surface pH values were measured bypotable pH meter before,and at 24 h,48 h,72 h after the first patch.Half an hour after the latter three detections of pH values,the skin response was evaluated clinically,as well as by transepidermal water loss (TEWL)and pH values,which were measured by pH-900 pH Meter.Results The responses to these solutions were similar between sensitive and normal skin groups.The order of skin surface pH values measured by the two pH meters was consistent with that of the original solutions.The skin surface pH value was altered by the synthetic urine,and this change was still present at 24 hours after the patches were removed.The TEWL values of skin challenged by synthetic urine were not higher than those by distilled water.The skin responses at 72 hours were more intense to the synthetic urines with pH values of.5,8.0,10.0than to distilled water.CondusionsSynthetic urines with different pH values can alter skin surface pH values,and skin responses to synthetic urines with a pH range 2.0-10.0 are similar to those to distilled water.