Recent research reveals that hot and humid weather is significantly more dangerous during pregnancy than heat alone. The study highlights the need for better heat warnings that account for humidity to protect vulnerable mothers and children.
Recent research shows that hot and humid weather during pregnancy poses a greater risk to a child’s health than heat alone, and the danger may be greater than previously believed. In a study published in Science Advances, researchers from the University of California, Santa Barbara explored how exposure to extreme heat and humidity during pregnancy affects children in South Asia.
Their findings were significant. When humidity levels were considered, the harmful effects of extreme heat on child health were approximately four times more severe than when only temperature was measured.
The reason is straightforward: humidity prevents the body from cooling down. When a pregnant woman is unable to release heat effectively, it can place serious stress on her body and negatively affect the development of her unborn child.
Why Humidity Makes Heat More Dangerous
The human body cools itself through sweating. As sweat evaporates, it removes heat from the skin. However, in humid air, sweat does not evaporate easily. This means that the body has a harder time cooling down, even at moderate temperatures.
Because of this, heat stress can occur at much lower temperatures when humidity is high. This is especially concerning during pregnancy, when a woman’s body is already under additional strain.
To accurately measure this risk, the researchers used a tool called the wet-bulb globe temperature (WBGT). Unlike regular temperature readings, WBGT takes into account humidity, air movement, and solar heat. It offers a more accurate representation of how hot conditions actually feel to the human body. The study reveals that relying solely on temperature readings greatly underestimates the danger, particularly in hot and humid regions.
Measuring the Impact on Children
To understand how these conditions affect children, the researchers analyzed height-for-age, a standard measure of long-term child health. Children who are much shorter than expected for their age are often experiencing chronic health issues that began in early life. Using large-scale public health surveys and detailed weather data, the researchers matched children’s health outcomes with the conditions their mothers encountered during pregnancy. They discovered that extreme heat alone had a negative impact. However, when heat and humidity were combined, the effect was significantly worse.
A child exposed to high heat and humidity before birth was, on average, 13% shorter than expected for their age. In contrast, exposure to extreme heat without high humidity resulted in only a 1% decrease. This clearly demonstrates how much humidity exacerbates the damage.
Why Pregnancy Is a High-Risk Period
Pregnant women are particularly vulnerable to heat stress. Their bodies produce more heat, and hormonal changes make it more difficult to regulate body temperature. And with high humidity, the risk increases significantly.
In early pregnancy, the developing fetus is highly sensitive to environmental stress. Damage during this time can affect the child’s growth and development for life.
In late pregnancy, the mother becomes more vulnerable. Heat stress at this stage can lead to preterm labour, resulting in babies being born too early and not fully developed. These children often face long-term health challenges that may not be fully overcome.
Why This Matters for the Future
This research has serious implications as climate change leads to more frequent and intense heatwaves. Many of the world’s most populated areas are hot and humid, especially near rivers and coastlines.
South Asia, which is home to over 1.7 billion people, is particularly at risk. The study suggests that millions of children could suffer lasting health damage over the next few decades if exposure to hot and humid conditions continues to rise.
Importantly, the study highlights a major gap in current health research. Most studies focus on deaths caused by extreme weather. However, many more people are affected than are killed, especially children whose health is impacted before they are even born. These hidden impacts can lead to lifelong health problems, reduced earning potential, and ongoing poverty, creating a cycle that can last for generations.
Small Changes Could Save Lives
Understanding the role of humidity opens the door to simple and effective solutions. Improved heat warnings that include humidity, better public education, access to cooling, rest, and shade for pregnant women, and early warning systems could all help reduce the risk. Even small interventions could have a significant positive impact.
To protect mothers and children in a warming world, we must also pay close attention to humidity. As this study shows, when it comes to pregnancy and child health, hot and humid weather is a far greater threat than heat on its own.