Chickenpox is a contagious virus that causes small, itchy, blister-like pustules all over the body, typically beginning on the stomach, back or face. Before this rash develops, other symptoms may be present, including fever, headache, fatigue and loss of appetite – but these may not occur until 10 to 21 days after a person's initial exposure to the varicella-zoster virus (VZV). While the virus normally causes mild illness, it can have serious complications, especially for those with compromised immune systems. Chickenpox is transferred from person to person by touching or breathing in virus particles. While once considered a normal part of childhood, chickenpox can now be avoided with a vaccine.