You can’t tell that Katrina Walker has a 50 percent chance of having a disease that could kill her in the next couple of decades.

The 28-year-old Michigan native likes to paint, read, and watch hockey; she recently posted on Facebook looking for manicure recommendations; she’s married, without kids, and is an activity assistant at a skilled nursing center.

Walker might also have Huntington’s disease, a degenerative disease that her mom has, giving her a 50 percent chance of having the Huntington’s gene. Huntington’s causes nerve cells in the brain to break down, and typically hits between the ages of 30 and 50, starting with mood changes and depression. In its latest stage it can cause an inability to speak or make voluntary movements. Most people diagnosed with Huntington’s die from complications of the disease, such as choking and pneumonia, on average 10 to 20 years after the onset of symptoms. Walker could take a test to find out if she has the gene, but she hasn’t yet.

Walker admits sometimes the possibility of having Huntington’s makes her anxious and sad, especially when she thinks of how it would affect her husband, or sees people with the disease at Huntington’s volunteer events, but for the most part, she doesn’t think about it, and doesn’t want to know if she has it. Not right now, anyway.

“If I have it, there’s nothing I or anyone else can do at this point,” Walker said. “There is no cure for it or anything right now that even controls the symptoms really well. Knowing isn’t going to prevent me from having it. I either have it or I don’t. At this point in life, I don’t need to know.”

By avoiding the medical test, Walker is part of a phenomenon referred to as information aversion, or the “ostrich effect” (which comes from the myth that ostriches, when in danger, bury their heads in the sand). It’s often used to describe people avoiding risky financial situations, like investors who check their portfolios less when the market’s bad, who were the subject of a 2009 study. But the term also applies to people avoiding medical tests.

Postponing getting a medical test could lead to a late diagnosis or unknowingly spreading a contagious disease. But living in uncertainty can also cause anxiety and affect how people choose to live their lives.

There are many reasons people might put off going to the doctor, according to Dr. Ghadeer Okayli, a psychiatrist in Austin, Texas who specializes in anxiety, depression, and mental illness. It could be that someone has social anxiety, and he’s afraid of being judged by doctors. Sometimes it could be caused by a panic disorder, if patients fear exhibiting physical symptoms like sweating or trembling if they go to a doctor. Someone might not have the time or money to see a physician. Or it could just be pure apathy. But for a large number of Okayli’s patients who avoid medical tests, they’re scared that a test will reveal a disease they have. It’s a form of denial, according to Okayli—they assure themselves they’re fine while worrying, deep down, that they’re not.

“Some people avoid tests because they don’t want to deal with the stress right now and just want to enjoy life,” said Okayli, who has worked with these kinds of patients for more than 15 years.

“Unnecessary stress or anxiety” was the top reason many college students gave for opting out of being tested for herpes in a study published earlier this year and led by Josh Tasoff, an economist at Claremont Graduate University, and Ananda Ganguly, an associate professor of accounting at Claremont McKenna College. Five percent of students in the study refused to take an HSV-1 test, for oral herpes (which causes cold sores), and 15 percent refused to take an HSV-2 test, for genital herpes (which causes genital sores), even though they were told their blood would be drawn regardless and the test results would be released confidentially. The students even chose to pay $10 to avoid this otherwise free test.

No one wants to find out they have herpes, a stigmatized disease that’s often the target of jokes and slut-shaming, but there are consequences to not knowing.

“In the traditional model of economics, the only reasons people want information is because it can help them make better decisions,” Tasoff said. “With HSV (herpes simplex virus), it does help one make somewhat better decisions. You can’t use the information to cure yourself, since no cure exists, but there are still actions you could take to improve your life, should an outbreak occur, to know how to deal with it and prevent others from getting it.”

Unknowingly spreading contagious diseases, like herpes, is one of the largest potential consequences of information aversion. When people avoid being tested for STDs or viral illnesses, it could be at the cost of someone else’s health.

And, of course, it could be at the cost of their own health, too. At what point someone gets diagnosed is not always the difference between life or death, for milder conditions, but it could make all the difference in diseases like HIV and cancer, which can prove fatal if not taken care of quickly enough. There are also long-term physical or mental effects that can be avoided by catching a disease early.

This is the case with autism spectrum disorders (ASD), a set of conditions that one in 68 kids are now diagnosed with, according to the Centers for Disease Control and Prevention (CDC), up roughly 30 percent from 2012. ASD can cause everything from trouble communicating and picking up social cues to repetitive body movements and seizures. It’s long been thought of, even by some today, as a hopeless disorder. But some kids actually “beat autism,” no longer exhibiting any of the symptoms of ASD, as the New York Times reported in July 2014. A few studies in the last couple of years have shown that with certain treatments, ASD symptoms can be improved, sometimes drastically. A study published in the September 2014 issue of Journal of Autism and Developmental Disorders even showed that intervention during infancy could lead to a less symptomatic form of ASD as kids age.

But women often don’t want to know if their babies will have ASD, as Dr. Harvey Kliman, a research scientist at Yale University School of Medicine, is realizing. Kliman led a 2013 study that analyzed 217 placentas. What they found was that abnormal folds and creases in the placentas signify a much higher risk of autism (almost 10 times higher).

Even though the test, analyzing a baby’s placenta after birth, can now be covered by insurance, he’s having difficulty finding women who want to take it.

“I thought it would be really popular,” said Kliman, who has been working on using the placenta to diagnose and predict autism and other developmental abnormalities for more than 20 years. “It didn’t happen. We went to birthing classes to promote it and they said we were making patients anxious. None of the obstetricians could get patients to do it, either.”

This mimics a September 2014 study showing that most women who knew the pros and cons of some prenatal tests chose not to take them. What Kliman eventually realized was that hearing your baby could have a much higher risk of autism puts a negative spin on the excitement, anticipation, and fear new parents are already experiencing. Given this, Kliman is beginning a huge marketing campaign to inform new parents about how beneficial it can be to begin intervention early, and he will be speaking with a group of pediatricians in October in hopes of getting their support.

Avoiding medical tests because of anxiety can cause more health problems, such as fatigue, muscle tension, restlessness, and difficulty sleeping, according to the Anxiety and Depression Association of America. Even if the worry is only an occasional one, Okayli said that a person’s anxiety could be suppressed, weakening the immune system and putting him or her at risk of depression.

This problem could be fixed by a simple doctor’s visit.

“When you face reality, you reduce your anxiety internally,” Okayli said. “It’s less painful to know you have a condition and deal with it than to deny it or agonize over the possibilities.”

But getting tested can also affect how someone lives her life. That was the conclusion of a December 2011 study, which showed that individuals at risk of Huntington’s who didn’t get tested lived as if they didn’t have the disease, in terms of major life decisions, and those who tested positive were more likely to get divorced, get pregnant, retire, report major financial changes, and change their recreational activities. Knowing your life expectancy is cut by 20 to 30 years is bound to cause some urgency.

For Walker, she’s optimistic about her chances. If she has Huntington’s, she’s not worried about passing it on, since she doesn’t plan on having kids. The time of her diagnosis won’t affect how the disease progresses. And though she admits she would feel more pressure to live life to the fullest if she tested positive for Huntington’s, she’s currently living her life as if she won’t die in the next couple of decades by this disease.

“Right now, I feel like my future is wide open and if I got tested and found out I have Huntington’s, I’d feel like, ‘Well, there’s my future, there’s my fate,’” Walker said. “Right now I have more time and freedom.”