Chickenpox. Young child suffering from a rash on its torso & face caused by chickenpox (varicella). In childhood, chickenpox is a mild infectious disease characterised by a rash and slight fever. It is caused by a herpesvirus which is transmitted by airborne droplets. After an incubation period of 11-18 days a mild fever develops followed by an itchy rash of dark red pimples which spread from the trunk to the face, scalp and limbs. The pimples develop into blisters that scab over and drop off after about 12 days. Treatment is bed rest, fever-reducing drugs such as Calpol, and the application of calamine lotion to relieve the itchiness of the rash and discourage scratching.