Why sharing a toothbrush or razor can lead to the transmission of blood-borne diseases (hepatitis b & c / hiv) although those items are regularly rinsed/ washed off after each use? is it cleaning with water & soap is insufficient to kill off virus?

Sharing a tooth brush, razor and hygeine items with someone with HIV, Hep B & C can increase your risk of becoming infected because body fluids may be present on these items. Soap and water will of course help in reducing the amount of virus on these items but because viruses are so small, it is not 100% safe or certain no virus remaining- it is best to not not share these items to begin with.

Sharing a toothbrush or razor can lead to the transmission of blood-borne diseases such as Hepatitis B & C and HIV, even if those items are regularly rinsed or washed off after each use. The reason for this is that these viruses can survive outside the body for a certain period of time, and cleaning with water and soap is insufficient to kill them off completely.