After a relaxing vacation, you’d think your body would be so rejuvenated that your immune system would be in tip-top shape. But it’s like clockwork: The second your plane lands back home, sniffles or body aches surface out of nowhere. How on earth can a week of sipping mojitos on the beach cause you to get sick when that’s the opposite of the point?

You’re not imagining that this is a common occurence. “I see patients that return from vacation sick quite often,” says pharmacist Inna Lukyanovsky. The CDC even has a special section of its website devoted to this phenomenon. Some people get sick before they even land at home, something so common that some doctors call it “leisure sickness.”

Whether you spend most of your vacation napping in a lavish hotel bed or walking miles through the streets of a new city, it’s certainly a change of pace from your life back home. That’s a lot for your system to adjust to, only for those changes to come to a grinding halt when you arrive back home again and jump right back into your usual routine.

Post-vacation illness is the ultimate letdown, but there are scientific reasons for it beyond the universe trying to make your transition back to the office grind as miserable as possible. Here’s the deal—and how to cope.

The Real Reasons You Get Sick

No, your body isn’t just doing this to torture you. Here’s why experts believe people get sick after vacation.

1. Planes (but Not for the Reason You Think)

Anyone with even mild germophobic tendencies cringes when boarding a plane. While it’s horrifying to imagine gross recycled air floating through the plane every time someone sneezes the next aisle over, that’s likely not the true cause of your health issues.

The real culprit behind most plane-related colds is the low humidity in flight. “Airplanes can be the worst,” pharmacist Lindsey Elmore says. “The low-humidity air can dry out nasal passages.” Thanks to the plane’s high altitude, you’re cruising through the sky in some seriously dry air. That dryness can irritate your throat and nose and can also make it tougher for your body to fend off bacteria.

The Fix: Over-the-counter saline nasal spray and some eye drops can go a long way to combating this issue.

2. The Usual Germy Suspects

It’s no surprise that the classic culprits, like being exposed to new allergens and germs, not washing your hands enough, and coming into contact with large crowds, can also make you sick on your travels. Airports, train stations, public transit, and tourist sites all put you in contact with big crowds, which can increase the likelihood of coming down with something.

“These days, with the ability to be in different hemispheres and continents so easily, transmissible diseases due to viruses and bacteria can easily spread to different regions quickly,” says Dana Hawkinson, M.D., assistant professor at the University of Kansas.

The Fix: The best thing to do is wash your hands regularly and for the right length of time (that’d be 20 seconds). You can also attempt to maintain some personal space in large crowds? Yeah, focus on the hand-washing.

3. Plain Old Exhaustion

The truth is, travel is freaking tiring. Even the most relaxing beach vacation in the world is fairly taxing to actually get to, especially if you’re the type who goes on a panicked frenzy to pack, complete your entire to-do list, and clean your house top-to-bottom the night before an early morning flight. (Raises hand.)

Before you even arrive at your destination, your body has likely already been subjected to several days of strain and exhaustion as you prepped for the trip, packed, and stuffed yourself into a tiny plane seat at an inhuman hour.

“Sleep deprivation is a major immune system depressant,” Inna says. “You often see people who spend sleepless nights on vacations or sleepless days when traveling for long hours.” This gets even more complicated when your vacation is in a different time zone. Jet lag is definitely not your immune system’s friend.

The Fix: Some effective time management can help you not freak out the night before a trip, and you can learn some ways to sleep better too.

4. Boozing It Up

There’s nothing wrong with celebrating on vacation—God invented swim-up bars for a reason! That said, the frustrating fact is that drinking more than you do during your non-vacay life can increase your likelihood of getting sick when you head home. “Excessive drinking during vacation can certainly inhibit your immune system and back up the detoxification system, leading to a virus or bacterial infections,” Lukyanovsky says.

The Fix: Consider spacing out your drinking with more low-key days in-between. If nothing else, stick to the old college trick of making sure you’re drinking a glass of seltzer or water for every glass of alcohol you drink. This will keep you hydrated (and help fend off hangovers).

5. Temperature Changes

Traveling between two different climates can confuse your body and make you more susceptible to illness. This is especially common if you jet off in the winter to lounge in a warmer destination.

“People traveling in the winter to a warmer climate often get sick coming back to cold weather,” Lukyanovsky says. “And the cold itself isn’t the reason; it’s the cold affecting the immune system response. That can trigger the virus that you normally would fight off without noticing.” In the moment, your body has bigger fish to fry—like readjusting to the cold—allowing viruses you’d normally fend off with no issue to creep in.

The Fix: OK, there really isn’t one for this, unless you want to start avoiding warm-weather destinations in winter (haha, no). But a little self-care won’t hurt…

Above All, Spoil Yourself

It’s not like you ever need someone else’s permission to treat yo’self, but remember that it’s extra important to coddle yourself when you get home from a trip. All of that flying and driving and time zone changing is a huge deal for your body. Whether you feel a cold coming on or arrive home feeling perfectly healthy, it doesn’t change the fact that your body needs to recalibrate.

If you can swing it, take a day off when you arrive home before heading back to work. On these days, give yourself permission to be a total couch potato. Laze around, do a relaxing exercise like yoga, and let your body adjust. Drink lots of water and eat fresh fruits and veggies. (Also pay attention to how you feel during this time. If you develop symptoms like persistent diarrhea, rashes, or a fever, check in with your doctor to rule out any pressing health issues that are linked to travel to certain regions.)

If you’re someone who struggles with letting yourself do nothing, remember that you’re doing this for your well-being! If you take the time to slow down, you’ll be a lot less likely to develop a surprise illness the second you dive back into your routine. The world keeps turning even when you sit still—promise. So kick up your feet, spend the day plotting your next vacation, and give yourself a high-five for putting your immune system first.