How your body is affected by humidity – and why you feel so bad

After weeks of drought in the UK, many are relishing the thunderstorms and rain showers of the past few days. But there is an unwelcome aspect to the dramatic change in weather: the attendant higher humidity has left skin feeling clammy and clothes feeling sticky. Relative humidity levels have been higher than average for the time of year, as high as 85 per cent on Thursday. What has caused the change and how does it affect our bodies? Shorts The summer so far has been so hot and dry because much of Britain and Europe has been dominated by stable high-pressure systems. But this week, a low-pressure system has been developing over Spain, sending warm, humid air northwards to the UK. This lets air pick up moisture from the Atlantic Ocean before it reaches the UK. Air that comes from the south is also warmer, and warmer air can hold more moisture. The humidity matters in summer, because the main way we cool down is by sweat evaporating from the body. When humidity is higher, that interferes with the evaporation process. “What matters is what happens to the sweat, because if you want to cool down, you want it to get evaporated,” said Dr Akshay Deoras, a meteorologist at the University of Reading. Hot and sweaty Humidity therefore has twin effects. It makes us feel more clammy, with our clothes feeling damp and sticking to us – and it interferes with our bodies’ natural cooling abilities. So it’s important that even if it isn’t as sunny as in previous weeks, we continue taking steps to make sure we don’t overheat, like using fans and keeping the curtains closed, said Dr Deoras. We may also get dehydrated because our bodies continue sweating, in a futile effort to cool down. “You release more and more of the sweat. You start getting dehydrated and your body temperature goes up,” said Dr Deoras. “If you are not able to cool down properly, then you can have heat exhaustion and heat strokes and potentially deaths – and that is directly connected to what is happening with humidity.” Asthma attacks High humidity can also make it feel harder to breathe, as well as triggering asthma attacks and exacerbations of the breathing condition, COPD. Even in those without any underlying health conditions, it can affect cognitive abilities. In laboratory tests at the University of Bath, at 27°C, volunteers performed worse on memory and attention tests when humidity was high, at 70 per cent. “In muggy conditions, participants reported higher mental workload, and productivity decreased by up to 20 per cent,” said Dr Sharareh Azar, a sustainability engineer who carried out the study. This was probably because people felt hotter and more uncomfortable, she said. “Tasks can feel more mentally demanding.” It is not clear how long the muggy conditions will last, as the weather is likely to be unstable over the next few days. Bands of rain and showers are moving across many parts of the UK, with the most persistent rain in the north-east, the Met Office has said. However, wind is likely to pick up over the weekend, which should make it feel less oppressive.