The objective of the study is to evaluate the viscosity of popular sclerosants and their flow hydrodynamics through a syringe/needle to further discuss Miyake's old, venous-capillary reflux theory, using additional objective data. The following sclerosing agents were tested in the study: 75% dextrose (D75%); 50% dextrose (D50%); 5% ethanolamine oleate (Etha5%); 0.5% laureth-9 (Aet0.5%) and 0.1% sodium tetradecyl sulphate (STS0.1%). Using 5 mL syringes and 27G needles, the resulting pressures and flows for each sclerosant agent were measured. To do this, a three-way stopcock was connected between the syringe and the needle so that an arm of the stopcock could be used to measure injection pressures with a digital monitor in 1 mmHg increments. Two trials were performed: in trial 1, the syringe was attached to a Samtronic 680 infusion pump and in trial 2, the solutions were injected manually. The observed sclerosant viscosities were as follows: D75%: 0.28 Poise; D50%: 0.12 Poise; Etha5%: 0.10 Poise; Aet0.5%: 0.07 Poise; and STS0.1%: 0.04 Poise. In trial 1 (constant flow), it was observed that D75%, which had the highest viscosity of the sclerosants tested, had the highest pressure readings. In trial 2 (constant pressure), the flow obtained with the D75% solution was lower than the flow of the other solutions. In conclusion, based on the rabbit study theory, vessel size and sclerosant viscosity and strength, not extravasation, play a role in causing ulceration from injection sclerotherapy. As a result, they all affect the potential of venous-capillary reflux being caused by sclerotherapy injection and, thus, the risk of postsclerotherapeutic cutaneous ulceration.