This work analysed the effects of para- phenylenediamine (p-PD), a component in permanent hair dyes products on the osmotic stability of human’s erythrocytes. Hemolysis was monitored by measurement of absorbance at 412 nm following addition of erythrocytes to NaCl solutions of varying concentration. Absorbance was fitted to sigmoid regression curves given by Boltzmann equation, and hemolysis was characterized by the NaCl concentration leading to lyses of 50% of cells (H₅₀), and by the intensity (H) and the amplitude of the lyses (dS). The parameters were determined in the absence and the presence of different doses of p-PD and at different times from 30 min to 2 h. The low doses of p-PD used in this study (5 µg/ml) protected human erythrocytes against hypotonic shock as evidenced by a decrease of H and H50 values compared to the control solution (p<0.05) for  2 h. However, the higher doses of p-PD used (2.5 and 3 mg/ml) enhanced hemolysis, since their H₅₀ values were higher than in the control group (p<0.05). In conclusion, it seems that the p-PD has simultaneously protector and haemolytic effects depending on the concentration used and the time of exposure.

Key words: Erythrocytes, hematotoxicity, membrane stability, p-phenylenediamine.