Confirmation Bias in Health and Disease Perception

Confirmation bias is a psychological phenomenon in which people tend to seek, interpret, and recall information in a way that confirms their existing beliefs or assumptions. This bias can significantly impact how individuals process health-related information, particularly when they are not well-versed in certain medical or scientific topics.

For example, someone unfamiliar with modern genetics may cling to outdated or oversimplified explanations of disease—perhaps attributing illness to lifestyle alone, or to environmental factors in isolation—while ignoring or discounting scientific evidence that points to genetic or epigenetic causes. This is not a failure of intelligence but rather a cognitive shortcut that helps people make sense of complex information by aligning it with what they already believe.

I personally became aware of the concept of confirmation bias through the work of Steve Gardner, whose explanations helped clarify why people may resist new scientific evidence, especially when it contradicts long-held views. Since 1994, I’ve believed in the significant role genetics plays in health. Learning about confirmation bias has helped me better understand why others might struggle to adopt this perspective.

The rise of genetic science has allowed us to look beyond outdated beliefs—like the once-popular notion of miasma, or “bad air,” as the cause of disease. Today, we know that genes and their expression (epigenetics) are fundamental to understanding the true causes of illness. However, without education in these areas, people often default to explanations that align with their worldview, even when those views lack scientific support.

This can be seen in debates about diet and health. For instance, human genetics support an omnivorous diet—our bodies evolved to process both plant and animal foods. Yet, some individuals adopt strict dietary philosophies, such as veganism, without considering how their unique genetic and epigenetic makeup might interact with such a diet. For some, the results are beneficial; for others, restrictive diets may lead to deficiencies or imbalances. But when confirmation bias is at play, people may ignore warning signs or dismiss contradictory data, focusing only on stories that support their beliefs.

Confirmation bias also affects how people view treatments. Pharmaceutical interventions are sometimes trusted without question or, conversely, rejected entirely. In both cases, bias can prevent a nuanced understanding. While medications can manage symptoms, they often don’t address the underlying causes, especially when those causes lie in complex genetic and environmental interactions.

Epigenetics adds another layer of complexity. Chronic stress and trauma, for example, can lead to changes in DNA methylation—a process that affects how genes are expressed. These epigenetic changes can trigger a cascade of health conditions, sometimes long after the original trauma occurred. Yet, if someone believes that mental health or emotional states don’t affect physical well-being, confirmation bias may cause them to reject this evidence entirely.

In German, confirmation bias is described as "die kognitive Verzerrung, Informationen so zu suchen, zu interpretieren und zu erinnern, dass sie die eigenen bestehenden Meinungen und Erwartungen bestätigen." This means people unconsciously seek out and favor information that supports their views, often ignoring or minimizing anything that contradicts them.

Key elements of confirmation bias include:

• Search for Confirmation: Individuals selectively look for data that supports their opinions. For example, someone convinced a particular group is harmful may only seek out negative news about that group.

• Selective Perception: People more easily notice, value, and remember information that aligns with their beliefs, while contradictory information tends to be forgotten or dismissed.

To move beyond confirmation bias, especially in health, we need to cultivate scientific literacy and openness to new information. Understanding the roles of genetics, epigenetics, environment, and psychology requires us to challenge our assumptions and be willing to revise them as new evidence emerges. In doing so, we not only gain a more accurate view of disease but also improve our ability to make informed decisions about our own health.

My blog offers a range of information on overlooked medical possibilities and missed clinical diagnoses, with a focus on often misunderstood or ignored factors—such as DNA variations and gene methylation—that, when not properly addressed, can hinder healing, fail to relieve pain, or even lead to further medical harm.

© 2000-2025 Sieglinde W. Alexander. All writings by Sieglinde W. Alexander have a fife year copy right. Library of Congress Card Number: LCN 00-192742