Angelina Jolie's chickenpox explained

She made the announcement in a video in which pink spots were visible on her face, neck and upper body.

"I just wanted to be clear and honest about why I will be missing the 'Unbroken' events in the next few days, which is that I found out last night that I have chickenpox. So, I will be home itching and missing everyone. And I can't believe it 'cause this film means so much to me," she says in the video published to Universal Studios Entertainment's verified Facebook page on Friday.

Chickenpox is a highly contagious disease. It is caused by the varicella zoster virus.

The virus causes an itchy blister-like rash that can be dangerous, particularly for people who get it late in life.

It is an airborne virus, so that means it can spread by breathing in the virus particles that come from the chicken pox blisters.

Chickenpox has become more rare since so many children have been vaccinated for it. The vaccine first became available in 1995.

Prior to availability of the vaccine, about 4 million people would catch it each year, according to the Centers for Disease Control and Prevention. About 100 to 150 died each year. More than half of those deaths involved adults. For adults who get chickenpox, there can be more serious complications like pneumonia. It can also be more severe for infants who get it.

For most people, especially for otherwise healthy children, it is a mild disease.

Other symptoms include a loss of appetite, headache, tiredness and fever.

If you've been vaccinated for it you should be immune. Typically, children get a first round of the vaccine when they are 12 to 15 months old. They get a second dose between the age of 4 and 6.

If you've had chickenpox before, you should have immunity for life.

If you haven't had it, and you haven't been vaccinated, it is not too late. The CDC suggests even as an adult you should talk to your doctor about getting the vaccine.

(CNN)