How did the 2 yuan erythromycin ointment become a

How did the 2 yuan erythromycin ointment become a "spot lightening expert"? The doctor gave the true answer

The awareness of health preservation is constantly improving, so many people will keep some commonly used medicine erythromycin ointment at home, which is one of the prices and affordable, and can be bought for about two yuan.Erythromycin ointment has good bactericidal and anti-inflammatory effects...