Health A to Z
Jet lag refers to a range of symptoms experienced while adapting to a different light-dark schedule following a flight to a new time zone.
It can affect people of all ages and is the result of your internal body clock not being able to adjust immediately to a new time zone.
Jet lag can disturb your sleep at night and make you feel drowsy and lacking in energy (lethargic) during the day. It can also sometimes cause digestion problems.
Crossing 7 to 12 time zones usually results in more severe jet lag than crossing 3 to 6 time zones. Crossing 1 or 2 time zones doesn't usually cause any problems.
People usually report more severe jet lag for easterly flights compared with westerly flights across the same number of time zones.
Jet lag isn't the same as general travel fatigue and can't be cured by certain types of aircraft, a more comfortable seat, speedy boarding, or the class of travel.
Read more about the symptoms of jet lag.
The world is divided into 24 different time zones. Your body's natural 24-hour clocks control 24-hour circadian rhythms, which are disrupted after crossing time zones.
Your body clocks influence your sleeping and waking pattern, as well as circadian rhythms in:
Your body clocks are set to your local time by light and social interaction, so that you're prepared for becoming active in the morning and for going to sleep at night.
If you travel across time zones, it can take a while for your body clocks to adjust to a new light-dark schedule and daily routine at your destination.
Read more about the causes of jet lag.
Jet lag can be a problem if, like pilots and cabin crew, you fly frequently across three or more time zones.
But there's little evidence to suggest that long-term human health is affected by jet lag. For example, the risk of most cancers is lower in commercial airline crew.
In most cases, jet lag symptoms pass after a few days without the need for treatment. Not many proposed treatments have been tested properly in clinical trials.
The advice below is a commonsense approach that might help reduce the effects of jet lag.
When you arrive at your destination:
Read more about treating jet lag.
It's not possible to prevent jet lag, and evidence about various treatments isn't very robust.
But there are some things that might be useful to help reduce its effects, such as changing your sleep routine a few days before departure and making sure you get enough sleep before you travel.
Read more about preventing jet lag.
The symptoms of jet lag can vary from person to person.
The severity of jet lag symptoms depends on the number of times zones crossed.
A long-haul flight across one or two time zones (for example, from the UK to South Africa) should cause little jet lag, but there will be general travel fatigue.
Most people only experience the symptoms of jet lag after crossing at least three time zones.
A disturbed sleep pattern is one of the most common symptoms of jet lag.
You may find it difficult to sleep at the correct times. For example, you may be awake at night and feel like sleeping during the day.
Other symptoms of jet lag can include:
Symptoms can last up to six days for some people who've flown across nine or more time zones, particularly in an easterly direction.
Jet lag occurs when the body has to adapt to a new light-dark schedule and normal daily routine after crossing several time zones.
Symptoms such as sleep disruption and tiredness are the result of your body finding it difficult to adjust to your new location's time zone because your body clocks can't adjust immediately.
Circadian rhythms are 24-hour variations in body functions, which are controlled by "biological clocks" in your body.
Jet lag occurs when your body's circadian rhythm needs to realign itself with a different light-dark schedule and daily routine.
The body's cells have their own clocks which interact with each other and are controlled by a "master" 24-hour clock in the brain.
The master clock helps to keep all the body clocks synchronised with each other and with the light-dark rest-activity schedule.
Your body is used to a regular routine of light and darkness at certain times of the day. But when you travel to a new time zone, this routine is disrupted.
Air travel makes it possible to cross several different time zones in just a few hours. After travelling so quickly, your body has to catch up and re-establish its circadian rhythm.
It takes time for your body to adjust the circadian rhythms to new times of light, darkness and eating.
Symptoms of jet lag are usually more severe when travelling east. This is possibly because your body finds it easier to adapt to a longer day (you "gain time" travelling west) than a shorter one (you "lose time" travelling east).
Your body is able to adapt better when you travel west because you're extending your day rather than shortening it when you travel east.
It's usually easier to delay sleep for a few hours than trying to force sleep when you're not ready to.
Factors that can contribute to general travel fatigue (which isn't the same as jet lag) include:
It's also thought high altitude and changes in cabin pressure may cause some symptoms similar to those of jet lag, regardless of travel across time zones.
Although the above factors can contribute to general travel fatigue, there's no evidence to suggest that they can make the symptoms of jet lag worse.
There are several things you can do to help reduce the effects of jet lag.
When you arrive at your destination, you should:
Melatonin is a substance (a hormone and neurotransmitter) that your body releases in the evening. It helps let your brain know it's time for your body to sleep.
Your body clock is synchronised to a daytime (diurnal) lifestyle by natural daylight and by the release of melatonin in your body. Social factors and possibly physical activity also play a part.
Melatonin is produced when it gets dark to help your body for sleep. Your body stops producing melatonin at around dawn to help you wake up.
Some jet lag remedies contain melatonin to help you sleep at night when your body is finding it difficult to adjust to the new time zone.
Melatonin has been found to help people sleep and reduce general feelings of jet lag in some, but not all, studies.
At the moment there's not enough evidence to say whether melatonin supplements are effective. Some people find them helpful, but they're not currently licensed in the UK for the prevention of jet lag.
There's also insufficient evidence regarding the possible side effects of melatonin for people taking the blood thinning medicine warfarin.
Because products containing melatonin aren't licensed, it's difficult to be certain how much melatonin they contain and whether other substances are present.
Some people find taking sleeping tablets can help relieve any difficulty sleeping (insomnia) associated with jet lag. But they're not usually recommended because of the risk of becoming dependent on them.
Sleeping tablets can also cause side effects, such as:
You may be tempted to look for jet lag remedies online. But take great care when buying medicines over the internet, particularly if it's usually only available on prescription. There's a risk of getting substandard or fake medicines that aren't safe or suitable to use.
If you're thinking about buying what may be a prescription-only medicine, you should consult your doctor, rather than buy the medicine direct from an internet supplier without a prescription.
The Medicines and Healthcare Products Regulatory Agency (MHRA) has more information about buying medicines online.
Jet lag can't be prevented, but you can try some strategies that may reduce its effects.
Some of these strategies have been studied in laboratory simulations of jet lag, but haven't necessarily been tested on people experiencing jet lag after real flights.
Before you travel:
During the flight:
Try to get some sleep if it's night-time when you arrive at your destination. You may find using ear plugs and an eye mask useful.
It may be better to stay on "home time" when taking a short trip of less than three to four days. If possible, arrange activities and sleep to coincide with the time at home.