Jet lag, also called jet lag disorder, is a temporary sleep problem that can affect anyone who quickly travels across several time zones.

Your body has its own internal clock, called circadian rhythms. They signal to your body when to stay awake and when to sleep.

Jet lag occurs because your body's internal clock is synced to your original time zone. It hasn't changed to the time zone of where you've traveled. The more time zones crossed, the more likely you are to experience jet lag.

Jet lag can cause daytime fatigue, an unwell feeling, trouble staying alert and stomach problems. Although symptoms are temporary, they can affect your comfort while on vacation or during a business trip. But you can take steps to help prevent or lessen the effects of jet lag.

Symptoms of jet lag can vary. You may experience only one symptom or you may have many. Jet lag symptoms may include:

• Sleep problems such as not being able to fall asleep or waking up early.
• Daytime fatigue.
• Not being able to focus or function at your usual level.
• Stomach problems such as constipation or diarrhea.
• A general feeling of not being well.
• Mood changes.

Symptoms are worse the farther you travel

Jet lag symptoms usually occur within a day or two after traveling across at least two time zones. Symptoms are likely to be worse or last longer the farther you travel. This is especially true if you fly east. It usually takes about a day to recover for each time zone crossed.

When to see a doctor

Jet lag is temporary. But if you travel often and experience jet lag, you may benefit from seeing a sleep specialist.

A disruption to your circadian rhythms

Jet lag can occur anytime you cross two or more time zones. Crossing multiple time zones puts your internal clock out of sync with the time in your new locale. Your internal clock, also called circadian rhythms, regulates your sleep-wake cycle.

For example, if you leave New York on a flight at 4 p.m. on Tuesday and arrive in Paris at 7 a.m. Wednesday, your internal clock still thinks it's 1 a.m. That means you're ready for bed just as Parisians are waking up.

It takes a few days for your body to adjust. In the meantime, your sleep-wake cycle and other body functions such as hunger and bowel habits remain out of step with the rest of Paris.

The effect of sunlight

A key influence on circadian rhythms is sunlight. Light affects the regulation of melatonin, a hormone that helps cells throughout the body work together.

Cells in the tissue at the back of the eye transmit light signals to an area of the brain called the hypothalamus. When the light is low at night, the hypothalamus signals to a small organ in the brain called the pineal gland to release melatonin. During daylight hours, the opposite occurs. The pineal gland releases very little melatonin.

Because light is so crucial to your internal clock, you may be able to ease your adjustment to a new time zone by exposing yourself to daylight. However, the timing of light needs to be done properly.

Airline cabin pressure and atmosphere

Some research shows that changes in cabin pressure and high altitudes associated with air travel may contribute to some symptoms of jet lag, regardless of travel across time zones.

In addition, humidity levels are low in planes. If you don't drink enough water during your flight, you can get slightly dehydrated. Dehydration also may contribute to some symptoms of jet lag.

Factors that increase the likelihood you'll experience jet lag include:

• Number of time zones crossed. The more time zones you cross, the more likely you are to feel jet lag.
• Flying east. You may find it harder to fly east, when you "lose" time, than to fly west, when you "gain" time.
• Being a frequent flyer. Pilots, flight attendants and business travelers are most likely to experience jet lag.
• Being an older adult. Older adults may need more time to recover from jet lag.

Auto accidents caused by drowsy driving may be more likely in people who are jet-lagged.

A few basic steps may help prevent jet lag or reduce its effects:

• Arrive early. If you have an important meeting or other event that requires you to be in top form, try to arrive a few days early to give your body a chance to adjust.
• Get plenty of rest before your trip. Starting out sleep deprived makes jet lag worse.
• Gradually adjust your schedule before you leave. If you're traveling east, try going to bed one hour earlier each night for a few days before your trip. If you're flying west, go to bed one hour later for several nights before you fly. If possible, eat meals closer to the time you'll be eating them during your trip.

• Properly time bright light exposure. Light exposure is a prime influence on your body's circadian rhythms. After traveling west, expose yourself to light in the evening to help you adjust to a later than usual time zone. After traveling east, expose yourself to morning light to adapt to an earlier time zone.

  The one exception is if you've traveled across more than eight time zones. Your body might mistake early-morning light for evening dusk. It also might mistake evening light for early-morning light.

  So if you've traveled more than eight time zones to the east, wear sunglasses and avoid bright light in the morning. Then allow as much sunlight as possible in the late afternoon for the first few days in your new location.

  If you've traveled west by more than eight time zones, avoid sunlight a few hours before dark for the first few days to adjust to the local time.

• Stay on your new schedule. Set your watch or phone to the new time before you leave. Once you reach your destination, try not to sleep until the local nighttime, no matter how tired you are. Try to time your meals with local mealtimes too.
• Stay hydrated. Drink plenty of water before, during and after your flight to counteract the effects of dry cabin air. Dehydration can make jet lag symptoms worse. Avoid alcohol and caffeine, as these can dehydrate you and affect your sleep.
• Try to sleep on the plane if it's nighttime at your destination. Earplugs, headphones and eye masks can help block noise and light. If it's daytime where you're going, resist the urge to sleep.

Jet lag is temporary and usually doesn't need treatment. Symptoms often improve within a few days, though they sometimes last longer.

If you're a frequent traveler bothered by jet lag, your health care provider may prescribe light therapy or medicines.

Light therapy

Your body's internal clock is influenced by sunlight, among other factors. When you travel across time zones, your body must adjust to a new daylight schedule. This allows you to fall asleep and be awake at the right times.

One way to adjust to a new daylight schedule is through light therapy. This involves exposure to an artificial bright light or lamp that mimics sunlight. You use the light for a specific amount of time when you're meant to be awake. Light therapy comes in a variety of forms, including a light box that sits on a table, a desk lamp or a light visor that you wear on your head.

Light therapy may be useful if you're a business traveler and are often away from natural sunlight during the day in a new time zone.

Medications

• Nonbenzodiazepines, such as zolpidem (Ambien, Edluar, ZolpiMist), eszopiclone (Lunesta) and zaleplon (Sonata).
• Benzodiazepines, such as temazepam (Restoril) and midazolam (Nayzilam).

You can take these medicines — sometimes called sleeping pills — during your flight and for several nights afterward as you adjust to a new time zone. Side effects are uncommon but may include nausea, vomiting, amnesia, sleepwalking, confusion and morning sleepiness.

Although these medicines appear to help you sleep better and longer, you may still feel jet lag symptoms during the day. The medicines are usually only recommended for people who haven't been helped by other treatments.

Sunlight

Being exposed to sunlight helps reset your internal clock. It's the most powerful natural tool for regulating the sleep-wake cycle.

Morning light exposure can usually help you adjust to an earlier time zone after traveling east. Evening light helps you adapt to a later time zone after traveling west.

Plan ahead to determine the best times for light exposure based on your departure and destination points and overall sleep habits:

• Before your trip. You can start light therapy up to three days before traveling to help you adjust to the new time zone once you arrive. If you're traveling east, try waking one hour earlier than your usual wake time and get at least one hour of light exposure. Do this daily until you leave for your trip, waking one hour earlier each day. Also adjust your bedtime to one hour earlier each night if possible. For westward travel, delay your wake and bedtimes.

• At your destination. If you've traveled east and crossed 3 to 5 time zones, try avoiding bright daylight first thing in the morning. Try to get several hours of bright light exposure in mid- to late morning.

  If you're crossing more time zones or traveling west, avoid bright light the morning of arrival but seek sunshine in the early afternoon. During the day, dark glasses can help block out light when you need to avoid exposure. At night, draw the window blinds or drapes or use a sleep mask. For each day on your trip, gradually shift your light exposure earlier.

Combining light exposure with exercise such as walking or jogging may help you adapt to the new time even faster.

Caffeine

Beverages with caffeine such as coffee, espresso and soft drinks may help offset daytime sleepiness. Choose drinks with caffeine wisely. Don't have caffeine after midday since it may make it even harder to fall asleep or sleep well.

Melatonin

As a sleep aid, melatonin has been widely studied and is a common jet lag treatment. The latest research seems to show that melatonin aids sleep during times when you wouldn't typically be resting, making it beneficial for people with jet lag.

Your body treats melatonin as a darkness signal, so melatonin tends to have the opposite effect of bright light.

The time when you take melatonin is important. If you've flown east and need to reset your internal clock to an earlier schedule, take melatonin nightly in the new time zone. You can take it until you adjust to local time.

If you've flown west and need to reset your body's internal clock to a later schedule, take melatonin in the mornings in the new time zone until you adjust.

A dose as small as 0.5 milligram seems just as effective as a dose of 5 milligrams or higher, although some studies show that higher doses are better at making you sleep. Take melatonin 30 minutes before you plan to sleep. Or ask your health care provider about the proper timing.

Side effects are uncommon but may include dizziness, headaches, daytime sleepiness, loss of appetite, and possibly nausea and disorientation. Don't drink alcohol when taking melatonin.

Additional possible remedies

Some people use exercise to try to ease the effects of jet lag.

If you want to try an alternative therapy, such as an herbal supplement, be sure to check with your health care provider first. Some therapies may interact with other medicines or cause side effects.