There is something about a rainy afternoon. The sky turns grey, rain taps against the windows, and suddenly the couch looks far more inviting than whatever you were supposed to be doing. So why does rain make you sleepy? The internet offers plenty of explanations, from melatonin and negative ions to falling air pressure. Some have reasonable science behind them; others sound scientific but do not hold up. The simplest explanation is probably the best: a rainy day usually means less daylight, less activity and a quieter environment, all of which make it easier to feel relaxed and less alert.
Less daylight is probably the biggest factor
Light is one of the most important signals for your circadian system, the roughly 24-hour body clock that helps coordinate sleep and wakefulness, which I explain in what is a circadian rhythm? Bright daytime light helps keep you alert and keeps your body clock in step with the day. A dark storm cloud does not turn the afternoon into night, but a heavily overcast day can be much dimmer than a sunny one, especially if you are indoors. A 2023 University of Manchester study that tracked 59 adults in their everyday lives found that more light over the previous few hours was linked to feeling less sleepy, according to the published study. So take away that light, and you remove one of the strongest signals telling your brain it is daytime.
This is also where melatonin comes in, though it is often exaggerated. Melatonin is the hormone that signals biological night, and light helps control when it rises and falls. But a grey afternoon does not trigger a sudden melatonin surge; your brain does not see a cloud and decide it is midnight. The better explanation is that dim days weaken the wakefulness signal, and if you are already tired, you notice.
Rain gives you a reason to slow down
This one sounds almost too obvious to count, but it matters. Rain changes what we do. We cancel a walk, skip the shops, stay inside and settle in with a cuppa or the television, so we get less physical activity and less stimulation. If you are already carrying some sleep debt, that quieter afternoon makes the tiredness you were ignoring much harder to ignore. There is a psychological side too: a warm house, dim light, a blanket and rain outside can become a powerful cue to relax. The rain may not be sedating you at all; it may simply be creating the conditions in which your normal tiredness becomes noticeable.
The sound of rain, and the noises it hides
Rain makes a fairly steady sound, quite unlike a car horn, a slammed door or a conversation, and many people find that soothing. It also works as a natural sound blanket, masking traffic, neighbours, dogs and other sudden noises that might otherwise grab your attention. Rain is often compared to pink noise, which contains a broad mix of frequencies with more energy in the lower tones than white noise. There is interesting research on pink noise and sleep, but it needs to be read carefully. A 2017 Northwestern University study of just 13 adults aged 60 and over played short bursts of pink noise, precisely timed to their slow brain waves during deep sleep, and found it increased their deep sleep and improved their memory the next morning, as the university reports. That is a fascinating result, but it is very different from lying in bed listening to a rainstorm. So rain sounds probably help some people relax, but they are not a proven sleep treatment.
The claims that do not hold up
The first is negative ions. Storms, waterfalls and rain do produce lots of negatively charged particles, and it is often claimed they improve mood, relaxation or sleep. But a 2013 review of 33 studies in BMC Psychiatry found no consistent effect of air ions on mood, anxiety, relaxation, sleep or comfort. It did find an effect on depression scores, but mainly at very high ion levels in people with seasonal or chronic depression, which is a very different thing from an ordinary rainy day making healthy people sleepy.
The second is falling air pressure. Rainy weather often comes with lower pressure, and some articles claim this means your body gets less oxygen and slows down. But normal weather-related pressure changes are small, nothing like the change you experience travelling to high altitude, and there is no strong evidence that they make healthy people sleepy. Some people do report headaches or aching joints when the weather turns, and researchers are still studying weather sensitivity, but that is not the same as showing that falling pressure causes rainy-day drowsiness.
A quiet, dim afternoon
So the answer is less exotic than the internet makes it sound. A rainy day combines less daylight, less activity, a steady background sound and a strong cue to relax, and together they give your brain fewer reasons to stay switched on. Negative ions and air pressure make for good stories, but the evidence for them is weak. And if the rain has you yawning too, there is more to that than tiredness, as I explain in why do we yawn?
This article is general information only and is not medical advice. If you regularly feel very sleepy during the day, whatever the weather, or struggle to stay awake when you need to be alert, speak to your GP.
Sources
- Didikoglu et al: Associations between light exposure and sleep timing and sleepiness while awake in a sample of UK adults in everyday life (2023)
- Northwestern University: Sound waves enhance deep sleep and memory (2017)
- Perez et al: Air ions and mood outcomes, a review and meta-analysis, BMC Psychiatry (2013)