Out of 129 nationwide cases so far this year, 58 are in California. Ten of those are in Los Angeles County, and 22 are in Orange County.
Doctors say measles can be much more serious than just a bumpy red rash.
"It can lead to ear infections, pneumonia; another complication would be encephalitis," said pediatric Dr. Lisa Kao.
So why the sudden outbreak? Experts say it has to do with the number of parents refusing to vaccinate their children. Last year in California, there was a 15-percent increase in the number of parents opting out of immunizations. In Orange County, health officials report a 30-percent increase.
Dr. Kao she gets the most questions about the measles, mumps and rubella (MMR) vaccine.
"MMR seems to have probably one of the worst reputations and so they tend to want to avoid that," said Kao.
Kao says the fears stem back to a recently discredited study linking MMR to autism. She often educates parents about the vaccine's safety.
The Centers for Disease Control and Prevention says many of the California cases are also a result of people visiting countries with measles outbreaks.
Dr. Kao hopes the rise in cases will convince more people to get the vaccine.
"And I'm hoping that not only will people reconsider vaccinating against the MMR, but also other vaccines like whooping cough. We're seeing a big surge of that too in the state of California," said Kao.
Last week, Long Beach public health officials reported 42 confirmed cases of whooping cough (pertussis). By comparison, last year there were 12 cases.
Like measles, pertussis is extremely contagious and is preventable by vaccine.