Firstly, monkeypox is caused by the orthopoxvirus whereas chickenpox is caused by Varicella-zoster virus which is highly contagious. Besides that, monkeypox patients will develop rashes within 1 to 5 days and it starts from the face and spreads to other parts of the body later. As for chickenpox, rashes can be observed on the chest, back and then on the face and the entire body. Anywhere between 250 to 500 itchy blisters may show up.