The amount of time the HIV rash lasts depends on the type and severity of the rash. The efavirenz rash typically lasts for about two to four weeks. Other rashes may last up to an indefinite amount of time due to drug resistance and other factors such as low immune system. Sometimes, patients develop a rash soon after becoming infected and it is located on the face and the trunk of the body. This rash also lasts for about two to four weeks.