How rising night-time heat is putting the body under constant stress

Even after sunset, the body may remain under heat stress as rising night-time temperatures disrupt sleep, recovery and the body's natural cooling process

  As cities continue to trap heat long after sunset, many people are finding little relief at night. Doctors warn that when the body cannot cool down properly during sleep, heat stress continues to build even after the day ends. Experts link this growing trend to climate change, urban heat islands and poor ventilation in crowded cities.

 

“Generally, the body experiences a slight reduction in temperature during the evening as it prepares for sound and restful sleep. But when temperatures remain high during the night, particularly under humid conditions, the body’s natural ability to expel excess heat becomes impaired,” said Dr Divya Gopal, additional director of internal medicine at Sir HN Reliance Foundation Hospital.

 

 

She explained this disrupts the body’s recovery process and can lead to insomnia, repeated awakenings, excessive sweating, dehydration and morning fatigue despite adequate sleep.

 

Why the body struggles to cool down at night

 

The human body naturally cools itself through sweating and by widening blood vessels near the skin surface. However, this process becomes less effective when the surrounding air remains hot and humid through the night.

 

Dr Bhanu Mishra, consultant- nephrology, Fortis Hospital, Shalimar Bagh, said heat from the body is released by sweating and dilation of blood vessels, but warm and humid air prevents proper heat dissipation.

 

“Lack of cooler night air makes it difficult for the body to release heat, making it difficult for the body to relax and have adequate rest,” he said.

 

Experts say humidity further worsens the problem because sweat cannot evaporate properly. Since evaporation is one of the body’s primary cooling mechanisms, the body remains overheated for longer periods, increasing heat stress and reducing the body’s ability to recover overnight.

 

How hot nights affect sleep, stress and overall recovery

 

Doctors caution that prolonged exposure to night-time heat can significantly affect sleep quality, health and mental wellbeing.

 

According to Dr Mishra, hot nights make it harder for people to fall asleep comfortably. This not only affects recovery from physical activity but also increases stress hormone production.

 

“There will also be high production of stress hormones like cortisol that causes excessive stress, inability to focus, poor response from the immune system, and hinder recovery from activities,” he noted.

 

Experts explain that high night-time temperatures disturb normal sleep patterns by reducing deep sleep and rapid eye movement (REM) sleep, delaying sleep onset and increasing repeated awakenings during the night. This becomes particularly concerning for people exposed to heat-intensive work during the day because sleep plays a crucial role in physical recovery.

 

Dr Gopal added that repeated sleep disruption caused by heat can gradually strain the cardiovascular and nervous systems, especially among vulnerable populations.  Experts also note that even a 1°C rise in internal body temperature can increase resting heart rate by around 10 beats per minute, placing additional stress on the body during prolonged heat exposure.

 

"Poor sleep further exacerbates fatigue, reduces productivity, increases risk of occupational injuries, and contributes to long-term health outcomes such as diabetes, high blood pressure, weakened immunity and mental health disorders," says Dr Mishra.

 

Who is more vulnerable?

 

Doctors say some groups are more vulnerable because their bodies struggle to regulate heat efficiently.

 

These include:

 

• Elderly people
• Infants and young children
• Outdoor workers exposed to daytime heat
• People with heart disease or diabetes
• Patients with kidney or respiratory illnesses

 

Dr Gopal explained that children and older adults have less efficient temperature regulation systems, while workers who spend long hours outdoors often carry excess body heat into the night.

 

Experts warn that dehydration, limited access to cooling spaces and poorly ventilated homes can increase health risks further.

 

How cities trap heat after sunset

 

Urban areas are especially vulnerable because concrete structures and roads absorb heat throughout the day and slowly release it at night. This phenomenon is commonly called the urban heat island effect.

 

“Concrete surfaces, roads, and other man-made structures absorb heat during the day and emit it during the night-time, thus resulting in higher night-time temperature,” said Dr Mishra.

 

Experts added that tightly packed buildings reduce airflow, while limited greenery and rising humidity make cooling even harder. As a result, temperatures in cities often remain significantly higher than nearby rural areas after sunset.

 

How to reduce the impact of hot nights

 

Experts recommend simple lifestyle measures to help the body recover better during heatwaves:

 

• Wear light cotton clothing
• Stay hydrated throughout the day
• Keep rooms ventilated
• Use fans or cooling devices
• Avoid alcohol, caffeine and heavy meals before bedtime
• Use blackout curtains during the day to reduce indoor heat build-up
• Take a lukewarm bath before sleeping

 

Cold showers can sometimes cause blood vessels to constrict, which may temporarily trap heat inside the body. In contrast, a lukewarm bath helps the body gradually lower its core temperature without shocking the system. It can also relax muscles and make it easier to fall asleep.

 

Doctors say while these steps may not completely eliminate heat stress, they can help improve sleep quality and reduce strain on the body during increasingly warmer nights.   

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This report is for informational purposes only and is not a substitute for professional medical advice.