How to Get Over Jet Lag: Light, Timing and Your Body Clock

Why jet lag happens

Your body runs on a roughly 24-hour internal clock. Its "master clock," the suprachiasmatic nucleus (SCN) in the hypothalamus, is set mainly by light. Normally it keeps pace with sunrise and sunset. But when you fly across several time zones in a few hours, it may be bright morning outside while your body still thinks it is the middle of the night.

The American Academy of Sleep Medicine (AASM) classifies jet lag as a circadian rhythm sleep disorder, usually a temporary one. The 2026 CDC Yellow Book describes it as insomnia or excessive daytime sleepiness with reduced total sleep after crossing at least two time zones, which may come with poorer daytime functioning, general malaise or stomach upset, typically within a day or two of arrival.

Why flying east is harder

The CDC explains that for most people it is easier to delay the body clock than to advance it, because the average intrinsic circadian period is slightly longer than 24 hours. Flying west means going to bed and waking later, which goes with the body's natural tendency. Flying east means sleeping and waking earlier, which takes more effort.

Using the averages the CDC cites, people adjust about 1.5 hours per day after westward travel and about 1 hour per day after eastward travel. Crossing six time zones eastward, full adjustment could take close to a week. Individuals vary widely; these are only averages.

Light: your most important tool

Your body clock is highly sensitive to light, and the timing of that light determines which way the clock moves:

• Morning light generally shifts the clock earlier, helpful after flying east when you need to sleep and wake earlier.
• Evening light generally shifts the clock later, helpful after flying west when you need to stay up later.

There is an important catch. Sleep researchers note that when you cross many time zones, the local morning during your first days may fall in your body's biological night, and bright light at that moment can push your clock the wrong way. For big time shifts, a personalised plan based on your origin, destination and flight times works better than intuition, and the CDC suggests using a jet lag calculator to time light exposure.

In practice: during a "seek light" window, spend time outdoors or by a bright window. During an "avoid light" window, dim indoor lights, cut back on bright screens and, if you are outside, consider sunglasses.

Before you fly and after you land

Drawing on the CDC Yellow Book, AASM resources and expert reviews, commonly recommended steps include:

• Shift gradually 2 to 3 days before departure: move bedtime and wake time about an hour per day toward destination time. Earlier for eastward trips, later for westward ones.
• Live on local time after landing: eat, move and sleep on the destination's schedule as much as you can.
• Nap briefly if needed: a 20 to 30 minute nap can help you stay alert; longer naps may make night sleep harder.
• Keep caffeine to the daytime: it can help alertness, but stop about six hours before bed.
• Drink water and go easy on alcohol: alcohol reduces sleep quality, and dehydration can make physical symptoms feel worse.
• Short trips may not need adjusting: the CDC notes that for stays shorter than about two days, you might keep to your home schedule instead.

About melatonin: some guidelines and reviews discuss timed melatonin for jet lag. However, in the United States it is sold as a dietary supplement and is not regulated by the FDA as a drug, so actual content may differ from the label, and data on interactions with other medicines are limited. Rules also differ between countries. Please talk with a doctor or pharmacist before deciding whether it is right for you and how to use it.

When to see a doctor

For most people, jet lag fades over several days to a week or two as the body adjusts. If your sleep is still off long after returning, if daytime sleepiness affects your work or safety, or if you cross time zones often (such as flight crew or frequent business travellers), a sleep clinic can help. If you have a chronic condition or take medicines on a fixed schedule, ask your doctor or pharmacist before travelling how to time your doses across time zones.

FAQ

How long does jet lag last?

Using the averages cited by the CDC, people adjust about 1.5 hours per day flying west and about 1 hour per day flying east, so more time zones and eastward travel mean more days. Individual differences are large, so treat these as rough guides.

Can I sleep during the day after arriving?

A short nap of 20 to 30 minutes can help you stay alert. Try not to sleep too long, or falling asleep that night may be harder.

Why is flying east more tiring than flying west?

Most people's internal rhythm runs slightly longer than 24 hours, so delaying the clock is easier than advancing it. Flying east requires sleeping and waking earlier, which usually takes longer to adjust to.

Should I take melatonin for jet lag?

Whether melatonin is appropriate, and when, depends on your health and other medicines. Please ask a doctor or pharmacist first, especially if you take other medication, are pregnant or have a chronic condition.

Do I need to adjust for a two- or three-day business trip?

The CDC notes that for trips shorter than about two days, you may keep to your home schedule. For longer stays, decide based on your itinerary.