One in 36 children in the United States has autism, according to the Department of Health and Human Services (HHS) but many dont learn theyre on the spectrum until adulthood.Those who grow up without a diagnosis can experience symptoms that are overlooked or misunderstood.One in every 45 adults in the U.S. is diagnosed with autism spectrum disorder (ASD), according to Autism Speaks, a national nonprofit for autism awareness.CANCER DRUG COULD DOUBLE AS AUTISM THERAPY, AND IS POISED FOR FDA APPROVALAlthough theres a current uptick in autism advocacy and education, there are likely "many adults" who never received a diagnosis or were misdiagnosed, the New Jersey-headquartered organization states on its website.If you think you or someone you love may be on the spectrum, heres what autism can look like in adults.ASD is defined by challenges with social communication and the presence of restricted or repetitive behaviors, according to the American Psychiatric Association.Some "hallmarks of autism" in adults as highlighted by Autism Speaks include feeling awkward in social situations, having difficulty understanding the feelings or thoughts of others, preferring to be alone, struggling with making friends and having trouble understanding social rules.RISING AUTISM RATES NOW AFFECT 3% OF CHILDREN, SAYS CDC REPORTSome verbal and non-verbal communication cues can include struggling with eye contact, responding in a "blunt way" or taking things literally.Repetitive or restrictive behaviors such as following the same routine every day, noticing small details that others wouldnt, and having "very intense and specific interests" are also signs of potential autism, according to the same source.Adults with autism may not display every characteristic, and behaviors and interests may change with age.BILL GATES LIKELY HAD AUTISM AS A CHILD, HE REVEALS: WASNT WIDELY UNDERSTOOD'Major life changes such as college moves, career transitions or changes in family status (like marriage, births, divorce or death) can cause symptoms to shift."Masking" is a term used in the autism community to describe the way an autistic individual hides symptoms to "fit in" and to avoid drawing attention in social situations.Some autistic people choose to mask to avoid bullying, maintain friendships and succeed at work or school, says Autism Speaks.It's possible to mask without even recognizing its happening, as some people adopt "subtle stimming behaviors," such as using fidget toys.Imitating the speech or body language of others during a conversation is another form of masking, along with forcing eye contact or facial expressions, which may feel unnatural.Masking can help autistic adults navigate daily interactions, but research has shown it can have negative effects on mental health, as it can lead to feelings of isolation and exhaustion, Autism Speaks reports.Autistic girls and women have been found to be more socially adaptive than boys and men with the disorder, making them more likely to mask, according to research.The Centers for Disease Control and Prevention has reported that autism is about three times more common in boys than girls.CLICK HERE TO SIGN UP FOR OUR HEALTH NEWSLETTERAlisha Simpson-Watt, a licensed clinical social worker, board-certified behavior analyst and founder of Collaborative ABA Services, said that masking often begins in childhood and can become "so ingrained that it feels like second nature."This can lead to many women going undiagnosed until adulthood."Cultural expectations also play a role, as girls are often socialized to be more accommodating, emotionally expressive or socially attuned, which can further obscure signs of autism," the Connecticut-based expert told Fox News Digital.ASD is a spectrum, which means symptoms can vary widely from one person to the next, said Simpson-Watt."While the core features remain the same, there are differences in social communication and repetitive behaviors," she said. "How the characteristics present can differ across individuals."Recognizing the "diversity of the spectrum" is key, Simpson-Watt emphasized. "Autism doesnt look the same in everyone, and understanding this can help more adults get the support and validation they need."For adults who believe they may have undiagnosed autism, the expert said it's important to "trust your instincts" and consider getting a formal evaluation.For more Health articles, visitfoxnews.com/health"Start by speaking with your primary care physician or checking with your insurance provider for a list of qualified professionals who diagnose autism in adults," she advised."Note that some insurance plans may have age-related restrictions on coverage for autism evaluations, so its helpful to start the process as early as possible."