The surprising reason morning sickness may be good for you and your baby

If you’ve ever felt queasy at the smell of coffee or turned away from a burger you once loved, you’re not alone. According to the National Institutes of Health, up to 80% of pregnant people experience nausea, vomiting, and food or smell aversions in early pregnancy. And a new UCLA study suggests these uncomfortable symptoms might actually be your body’s way of protecting both you and your baby.

For many, morning sickness can feel confusing or even isolating. But researchers say it may be a sign of a healthy, finely tuned immune system working behind the scenes. Rather than signaling trouble, your body may be sending helpful warnings designed to keep you—and your developing baby—safe.

Related: When does morning sickness start?

The science behind morning sickness

At UCLA, anthropology professor Molly Fox and her colleagues Daniel Fessler and Dayoon Kwon followed 58 pregnant women in Southern California, collecting blood samples and tracking symptoms such as nausea, vomiting, and aversions to certain foods and smells.

They measured immune proteins called cytokines—molecules that regulate inflammation and immune responses—and found that women experiencing nausea or food aversions showed a shift toward a pro-inflammatory immune response. In plain language, their bodies were actively protecting themselves while also preventing an immune attack on the fetus—a delicate act of biological diplomacy.

Nausea and aversions may even encourage pregnant people to avoid foods or substances that could be harmful during the early, most vulnerable stages of fetal development. While the findings are correlational and more research is needed, the pattern supports a long-standing theory that pregnancy nausea is a protective adaptation.

An evolutionary perspective

Humans have one of the most invasive placentas of any species, meaning fetal cells are bathed in maternal blood. This intimacy requires special immune strategies to prevent the body from rejecting its own developing baby.

Scientists believe that morning sickness may be one such adaptation: a behavioral mechanism shaped by natural selection to minimize exposure to harmful foods or environmental toxins. 

Odors and tastes that trigger nausea—like tobacco smoke, strong cheeses, or undercooked meat—may not be random irritations. They could reflect evolution’s way of nudging pregnant people away from potential dangers, a survival strategy written into our biology.

Related: 4 lies I believed about morning sickness—before I had it myself

Practical takeaways for parents

Reframing morning sickness as meaningful can help reduce stigma and guilt. Morning sickness is your body’s built-in shield, actively working to protect new life. Recognizing this can empower pregnant people to:

• Advocate for accommodations at work. While the study itself didn’t test workplace outcomes, understanding that morning sickness has biological underpinnings could support requests for flexible schedules, remote work options, or more frequent breaks.
  
• Communicate with healthcare providers. Knowing that symptoms are often normal can guide conversations about safe coping strategies.
  
• Practice self-compassion. Your body is performing an extraordinary feat. Acknowledge that it’s okay to slow down when needed.

Related: It’s science: Probiotics in early pregnancy may reduce morning sickness

Why it matters

Each bout of morning sickness is a sign of the remarkable resilience and protection your body provides. Seeing nausea and aversions as part of a larger story of evolutionary and immunological strategy can help you feel validated, empowered, and connected to your own body’s remarkable work.

The next time you turn away from a smell or feel queasy in the morning, remember: your body  is acting in your and your baby’s best interest—a fascinating testament to the ways humans have evolved to protect new life. Morning sickness may be uncomfortable, but it’s also a sign of care, resilience, and survival written into your biology.

Sources:

1. Gastroenterology Clinics of North America. 2011. “Nausea and Vomiting of Pregnancy”
2. Evolution, Medicine, and Public Health. 2025. “Of scents and cytokines: How olfactory and food aversions relate to nausea and immunomodulation in early pregnancy”