5 Things Scientists (Not Celebs) Say May Cause Autism

Measles, a once eradicated disease, is making a comeback. More than 100 cases have been reported across 14 states since the Disneyland outbreak began last December—forcing health organizations, public health agencies, and concerned individuals to beg parents everywhere to vaccinate their children.

The public has blamed celebrities such as Jenny McCarthy, Rob Schneider, and Kristin Cavallari. After all, they've irresponsibly used their influence to speak out about a link between vaccines and autism (a myth that can be traced to a discredited 1998 study whose author's medical license had since been revoked). But the measles crisis is in the hands of families now, and there's one major thing they can do: Listen to the experts.

On Friday, advocacy group Autism Speaks released a statement.

"Over the last two decades, extensive research has asked whether there is any link between childhood vaccinations and autism," Rob Ring, the organization's chief science officer, said in the statement. "The results of this research are clear: Vaccines do not cause autism. We urge that all children be fully vaccinated."

Other autism advocates agree.

"What we've learned is that autism likely starts long before the emergence of any type of symptoms that can be observed," said Christopher Smith, a psychologist specializing in autism diagnosis and the vice president and research director at the Southwest Autism Research and Resource Center. "The cause of this? We have no idea," he said. Like Ring, one thing he knows "without a doubt" is that vaccines don't cause the disorder.

As advocates focus on how to best serve people with autism, many scientists are working to understand the disorder. Here are five things experts say may cause autism.

1. Genetics

According to the National Institutes of Health, families with one child who has autism have about one in 20 chances of having a second child with the disorder. Researchers have yet to pinpoint the exact reasons, and a study recently published in Nature Medicine—claimed to be the biggest autism genome study so far—finds that siblings with autism carry different risk genes.

2. Pesticides

Pregnant women who reside within a mile of areas where pesticides are sprayed increase their offspring's chances of developing autism and learning disabilities, according to a study published in June 2014 in Environmental Health Perspectives. The team from the University of California, Davis, tracked 1,043 families in California, where there's a $38 billion agricultural industry. One-third of the pregnant mothers in the study lived within a mile of farms that used pesticides linked to impaired development. "Proximity to organophosphates at some point during gestation was associated with a 60-percent increased risk for ASD,” the authors wrote in the study.

3. Air Pollution

In a study published in Environmental Health Perspectives in December 2014, researchers from Harvard links autism risk to a mother's exposure to air pollution during pregnancy. The team analyzed data from more than 100,000 women, including the air quality of where they lived before, during, and after their pregnancy, as well as their distance from freeways and other air-contaminant hot spots. The result: The higher the exposure during a mother's third trimester, the higher the chances of autism—especially in baby boys. Risk doesn't equal cause, but advocates think the findings justify improving air-quality regulations.

4. Some Medications

A 2005 study published in the International Journal of Developmental Neuroscience links autism risk to two medications. One is thalidomide, which was pulled from the market as a sickness, anxiety, and insomnia drug after being associated with birth defects but is still used to treat multiple myeloma and leprosy. The other is valproic acid, a medication prescribed to treat seizures or bipolar disorder.

5. Parents' Age

Scientific consensus says that autism risks increase with parental age, but which parent has more impact is debated. According to UC Davis Health System researchers who studied all births in California during the '90s, a 40-year-old woman has a 50 percent greater risk of giving birth to a child who will develop autism than a woman age 25 to 29. But another study, published in Nature in 2012, says that a mother's age has no effect on autism risk. However, men in their 40s or older who father children carry a roughly 2-percent risk.