At 2am on Sunday night the clocks go back an hour in the UK…

A clock. In daylight.

That means people all over the country will wake up confused as to why their phone clock no longer matches their watch (but also happy that they are now in the half of the year where their oven clock is correct). The problem is, while your phone probably updates itself, and your watch can be changed pretty easily, the body’s inbuilt clock is a bit harder to control.

Body clocks exist in plants, bacteria, fungi and animals, and are vital for our health and survival. As well as a centralised clock in our brain, tissues all around our body contain their own time-keepers. This means that along with the drive to sleep, all sorts of other processes are affected by time of day – from metabolism to blood pressure.

When the clocks go back, your internal clock no longer lines up with the external world. Your body may think it is 7am, and time to get up, but the clock says 6am. While this seems great (an extra hour of Sunday, yay!), it could have a knock on effect, making it harder to stay awake in the evening. This is a mild form of jet-lag. When you travel to another time-zone, your body clock is dramatically out of sync, and it can take days to get back to a normal sleep pattern.

Interestingly, if animals are left to behave solely as directed by their body clocks, they often don’t stick exactly to a 24 hour day. This is known as ‘free running’ and means all external cues, from light to temperature to social interaction, must be removed. When this has been done on humans, people quickly find themselves drifting away from outside time, and may end up hours out of sync in a matter of days.

Roosters, like many animals, don’t give a good Goddamn what your watch says.

Luckily, most of the time we don’t have to rely just on internal time-keeping. Our body clocks have a reset switch, and it is controlled by light. During the day, bright light is detected by special cells in our retina, which send signals to the suprachiasmatic nucleus in the brain’s hypothalamus. This initiates all the changes that make us feel awake and alert.  As dusk approaches, this same system switches our body to rest mode, and increases the release of melatonin, a hormone which makes us feel sleepy.

This system worked brilliantly for our ancestors, who timed their day by the sun, but in the modern world we can often end up out of sync. Many of us find it very hard to wake up on a dark winter’s morning, and this is hardly surprising as our body isn’t getting the light cues it needs to switch off melatonin production. Equally, if you expose yourself to bright lights in the evening, particularly if they are blue-tinged, like the light from a phone or laptop, it can delay the sleep-induction process, and may even cause insomnia.

One benefit of the changing clocks is that the mornings will be lighter (for now at least). This is good news- waking up is much easier when it is light outside. Getting some sunshine as soon as you wake up can also help reset your body clock, making sleep easier that night. But with sunset coming an hour earlier, you may find yourself feeling sleepy earlier than normal, as your melatonin levels rise.

Scrooge would’ve had an even worse night if the clocks had gone back half way through.

If you are an evening person, you probably won’t be too badly affected by the autumn clock change, but morning people might struggle more to adjust, waking up early and feeling tired and lethargic in the evenings. Those with small children may also be more affected, as toddlers might not relish the extra hour in bed as much as adults do!

The good news is that it shouldn’t take long for your body’s internal clock to catch up, and these processes to settle down. And if you do need a bit more of a boost, getting some daylight in the afternoon is a good way to keep yourself feeling alert into the evening.

Ginny Smith is a science presenter and writer. A Natural Sciences and Psychology graduate of Cambridge, Ginny performs science shows all over the world and presents a wide range of science content for the likes of the Cosmic Shambles Network and the Naked Scientists. She is the co-author of three DK Publishing books looking at science, food and the human body. She is @GinnyFBSmith on Twitter.

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