What Causes Autism and Why Are More and More Kids Being Diagnosed With It?

Autism Awareness ribbonDoes a friend or family member have a child with autism?  Autism rates seem to be skyrocketing.  Among children who are 8 years old, autism has nearly doubled  from 1 in 150 (for children born in 1992) to 1 in 68 for children born in 2002.[1]

Autism is part of a larger group of related conditions, called autism spectrum disorders (ASDs), all of which usually involve delayed verbal communication and difficulties in social interactions.  Studies suggest that children with autism tend to have other problems with how their brain functions, with as many as 20-30% developing seizures or epilepsy.

What Causes Autism?

The exact cause or causes of autism are still unclear, and some theories have sparked controversy, such as the role of vaccinations (see our article on vaccination safety here) or the importance of dietary factors such as gluten (see our article on gluten here.)  There is clear evidence for a possible genetic link.   Autism and related conditions seem to run in families; if one identical twin is diagnosed with autism, the other twin has a much higher chance of also having autism.  We also know that children who are born prematurely have a greater chance of being autistic, and children with older fathers are at slightly higher risk of autism.[2] [3]

While genetic causes of autism are still being investigated, other studies suggest that certain environmental exposures in the womb may increase the chances of a child developing autism. In addition, certain geographical areas of the country have much higher rates of autism, such as California, Texas, North Carolina and Utah.[4] Are doctors or parents in these states quicker to suspect and diagnose autism, or is something else going on that is causing more kids to develop autism?

States that require a physician or psychologist to diagnose autism for families to qualify for special education benefits tend to have lower overall rates of autism. It’s also true that children who live in urban areas and whose parents are better off are more likely to be diagnosed with autism,  but again that finding doesn’t explain the higher rates of autism in California, Texas, North Carolina and Utah. Some scientists have suggested that higher amounts of environmental toxins in these areas may explain the relatively high rates of autism.[4]

New Research on Autism and Our Environment

Sex hormones, medications, certain metals such as lead, pesticides, and chemicals used to make plastic hard or pliable have long been suspected of having a role in autism.[4]  They have not been proven to cause autism, but these are known to trigger or worsen other health problems, including some that affect the brain.  Many studies have shown that chemical exposures during development in the womb can have much more serious health effects than the same exposures would in adults.

A large 2014 study investigated the connection between autism and genital malformations using health insurance claims from almost a third of the U.S. population.[4] Like autism, genital malformations are increasing: cases of undescended testicle(s) increased 200% between 1970 and 1993, and the percentage of boys born with a deformity of the penis known as hypospadia doubled.[5] [6]  Many studies have shown that these malformations are more common among children whose mothers have high levels of chemicals that affect the hormones in their bodies, such as phthalates which are found in cleaning products, medicines, and personal care products like shampoos and creams (see our article on phthalates here.) The link between these chemicals and genital malformations has surfaced in other studies, particularly those involving women in professions (chemists, health care workers, housekeepers) that require working daily with these chemicals.[7] [8] [9]

The 2014 study based on insurance claims found that boys born with genital defects were much more likely to be diagnosed with autism.  Boys with autism spectrum disorders (ASD) were 5.5 times more likely to be born with genital malformations than males without ASD.  However, there was no connection between genital malformation and intellectual disability. A similar pattern was observed for girls, but the connection wasn’t as strong.  No one knows why but, ASD is 5 times more common in boys than girls.

As found in previous studies, the children with autism in this study were more likely to live in cities and be from families with higher income. For every additional $1,000 in income above the country average, the rate of autism went up by about 3%. A similar trend was seen with measurements indicating how urban a household’s location was. However, city-living and wealth had a much weaker connection to autism than genital malformations.

While this study doesn’t prove that exposures to chemicals in our environment cause autism, it suggests that whatever is behind the increase in genital malformations could be behind the increase in autism. Researchers need to continue to investigate the possibility that environmental exposures are contributing to autism.

Diagnosis of Autism: What We Do Know

Autistic children benefit from early diagnosis, preferably in the first two years of life.  Early diagnosis allows behavioral therapy or other treatments to begin early when it seems to be most effective.  If you are concerned about your child, talk to your doctor about a referral to see a specialist who can help determine if follow-up is needed.  Signs of autism may include symptoms such as:

  • no babbling or pointing by age 1
  • no single words by 16 months or two-word phrases by age 2
  • no response to name
  • loss of language or social skills
  • poor eye contact
  • excessive lining up of toys or objects
  • no smiling or social responsiveness[10]

A final diagnosis should be made by a team of qualified professionals including a neurologist, psychologist, psychiatrist, and speech pathologist.  The outlook for children with autism is improving as we learn more, and many children can improve significantly within a few years of treatment.

Parents should also be aware that the FDA has released warnings about unproven treatments for autism, such as hyperbaric oxygen therapy, chelating agents, and other probiotics and supplements which claim to help cure autism. See the FDA report here.


All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.

The National Center for Health Research is a nonprofit, nonpartisan research, education and advocacy organization that analyzes and explains the latest medical research and speaks out on policies and programs. We do not accept funding from pharmaceutical companies or medical device manufacturers. Find out how you can support us here.


  1. Centers for Disease Control and Prevention. 2014 ASD report, Prevalence of Autism Spectrum Disorder Among Children Aged 8 Years — Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2010.
  2. Kong A, et al. Rate of de novo mutations and the importance of father’s age to disease risk. Nature. 2012; 488(7412):471-5.
  3. Leavey A, et al., Gestational Age at Birth and Risk of Autism Spectrum Disorders in Alberta, Canada. J Pediatr. 2013; 162(2):361-8.
  4. Rzhetsky A, et al, Environmental and State-Level Regulatory Factors Affect the Incidence of Autism and Intellectual Disability. PLOS. 2014; 10(3): 1-11.
  5. Paulozzi L, et al.  Hypospadias trends in two U.S. surveillance systems. Pediatrics. 1997;100(5):831–34.
  6. Lund L, et al. Prevalence of hypospadias in Danish boys: a longitudinal study. European Urology. 2009; 55(5):1022-1026.
  7. Lin S, et al. Maternal occupation and the risk of major birth defects: A follow-up analysis from the National Birth Defects Prevention Study. Int J Hyg Environ Health. 2013; 216(3): 1-15.
  8. Garlantezec R, et al. Maternal occupational exposure to solvents and congenital malformations: a prospective study in the general population. Occup Environ Med 2009; 66:456-463.
  9. Herdt-Losavio ML, et al.  Maternal occupational exposure to solvents and congenital malformations: a prospective study in the general population.  Occup Environ Med 2010 67: 58-66.
  10. National Institute of Neurological Disorders and Stroke. Autism Fact Sheet. Accessed April 17, 2014. https://www.ninds.nih.gov/Disorders/All-Disorders/Autism-Spectrum-Disorder-Information-Page