Lucky are the few who haven’t gone on a much-needed holiday only to spend their vacation hugging a box of tissues in a bed-bound Theraflu blur. So commonly do people seem to fall ill on vacation that some psychologists have christened it ”leisure sickness.” According to a leading hypothesis, during the work crunch that tends to hit right before a vacation, your immune system kicks into overdrive. Once you’re safely en route to your holiday destination, however, it lets down its guard—and a sore throat and stuffy nose soon follow. 
 
 It sounds like a reasonable enough theory. The Dutch psychologist who coined the term documented its prevalence in a 2002 study that asked 1,900 people whether they tended to fall ill on vacations and weekends; about 3% of them said they did. Only there are no actual medical studies to back this up. 
 
 The more plausible reason so many of us seem to wind up vacationing in a sickbed? Travel itself. 
 
 “Whether influenza, the common cold, or other viruses, it’s really quite clear that mass transportation contributes to transmission,” says William Schaffner, a professor of preventive medicine at Vanderbilt University Medical Center. “It’s not the only way, but it’s a major way.” 
 
 Once temperatures drop, we start encountering influenza and the scores of common cold viruses in our daily lives at a much higher rate. (Though scientists aren’t totally sure why, these viruses thrive in cold weather.) 
 
 While flu activity in the US tends to peak in February, says Schaffner, it varies a lot. In 2009 and 2013, outbreaks got going as early as November. The chart below shows the level of outpatient activity for patients with flu-like symptoms based on US Centers for Disease Control and Prevention tracking: 
 
 These viruses are thought to spread through cough- and sneeze-borne droplets, through inhalation, or when we come into contact with surfaces on which they land and then touch our eyes, nose, mouth, or other mucous membranes. As these bugs circulate a local area during cold months, we build up antibodies that help us fight off those viruses throughout the rest of the season. 
 
 Our immune system’s defenses don’t help much in an airport, though, where new viruses from all over the planet abound. Worse, you’re likely getting much nearer than usual to these germ-ferrying fellow travelers—and for unusually long periods of time. 
 
 The aircraft cabin is an obvious example, though the air conditioning system prevents most germs from cycling through the cabin. Still, those sitting within a two-seat radius of a sick passenger—two seats in front, behind, and to the side—stand a greater chance of catching the bug. The cabin air’s relatively low humidity also promotes transmission, says Schaffner. 
 
 But cabins are hardly the only source of risk. The flu and common cold viruses spread more easily in any crowded area. Travelers also spend a long time in close contact with each other while in line at security, waiting at the gate, and while boarding the plane. While there’s minimal research on other forms of mass transport, they likely present similar transmission dynamics. 
 
 As it happens, a cold virus itself doesn’t send mucus streaming from your nose and make your head feel huge. Instead, your body’s battle against the virus inflames tissue, causing these and other common cold symptoms. Normally, the stress hormone cortisol helps keep your body’s inflammation in check. When a person is worn down by chronic stress, however, the body responds less and less to cortisol. The runaway inflammation that results makes for more extreme cold symptoms. 
 
 “The explanation seems sensible in that stress will cause release of corticosteroids and they may help us during the stressful period but they may also lower our resistance to infection and maybe this is a delayed response,” says Dr. Ronald Eccles, director of Cardiff University’s Common Cold Centre, who has been asked about the phenomenon from time to time. 
 
 Is that a slam-dunk argument in favor of the “leisure sickness” phenomenon? Not exactly. 
 
 Research by Sheldon Cohen, a psychology professor at Carnegie Mellon University and pioneer in the study of the effects of stress on the immune system, has shown that enduring chronic stress or an acutely stressful event—including work-related experiences—leaves one’s body more vulnerable to cold viruses. “However,” Cohen says, “I’m not aware of any evidence that people are more susceptible to disease post-stressor.” He adds that the psychological effects of extremely stressful events may linger long after the cause itself recedes. 
 
 It’s possible some psychological biases are at play as well. 
 
 “I’d guess that people remember illnesses during vacations better than those that occur during more regular work schedules,” says Cohen, adding that these incidents might not actually be more prevalent. And as Vanderbilt’s Schaffner points out, we don’t hear from stressed-out masses who don’t get sick on their vacations. 
 
 Regardless of your belief in “leisure sickness,” the best thing to do for your immune system is to get an annual flu vaccine, says Schaffner. Those that haven’t yet might want to get cracking. The strain that seems dominant this year “is on the severe end of the spectrum,” he says. ||||| It's no fun being ill on holiday. So why do so many of us succumb every time we finally wind down? Emine Saner finds out how to break the cycle 
 
 Cath is a lawyer. She regularly works 14-hour days, often takes work home with her and lives with a fairly constant level of stress. She had been working on a big deal for weeks and once it was finalised, she took a day off and came down with a kidney infection. "Something always happens whenever I stop work," she says. "I've seen it happen to my colleagues too. You have a totally manic period at work and then you stop, feel exhausted and come down with flu. I went on holiday earlier this year and spent the first three days asleep." 
 
 This is a fairly typical example of what one psychologist has termed "leisure sickness" - becoming unwell on holiday or at the weekend. Usually, the symptoms are cold or flu-like and include nausea, migraine, headaches and muscular pain. Professor Ad Vingerhoets, from the department of psychology and health at Tilburg University in the Netherlands, started researching the concept of "leisure sickness" after becoming aware that he suffered from it himself. "I noticed that I was never ill, except occasionally, and then the problems started on Friday at 5pm, and by Monday morning, I had recovered," he says. "The period between Christmas and new year seemed to be my favourite time to get ill." He asked around and found that other people had similar experiences. 
 
 After conducting his survey of more than 1,800 people, he estimated that around 3% of people suffer from "leisure sickness". Vingerhoets found that many of those who experienced it shared similar personality traits - they were perfectionists in their work, preoccupied with achievement and took their professional responsibilities very seriously, making it harder to leave it behind. "I think there are three main explanations for it," says Vingerhoets. "It may be related to a change in habits during the weekend or on holiday, including more or less sleep, coffee or alcohol. Or that during work, our busy jobs direct the brain's attention away from signals from the body, so when you go to a quiet setting, those signals are suddenly perceived and interpreted as symptoms." 
 
 The third theory is that when you have been busy at work or stressed, your body stays "activated" during the time when you should be resting. "We found that the people with many vague complaints failed to reduce their energy production, or adrenaline. It seems obvious that needless energy may compromise our health and weaken our natural defences." 
 
 It is now widely believed that stress can affect the immune system. "When you are in a state of stress, your immune system will become depressed, leaving you susceptible to illness," says Neil Shah, director of the Stress Management Society. "You rush around, and when you stop, your body is still reverberating from it. If you're on holiday, you're probably eating food you don't normally eat, drinking more alcohol than usual, being in the sun or doing activities, sightseeing or exercise when you're not used to it, and your body might not be able to cope, which is why people get ill." 
 
 One of the most common symptoms of leisure sickness is migraines. Dr Anne MacGregor, director of the City of London Migraine Clinic, says it has been well recognised that migraine attacks frequently occur during downtime. "We think it's a let-down response. Your body copes with stress because you can see the weekend or a holiday in sight." Then, when you stop, it catches up with you. "When people are operating under stressful conditions, they don't tend to get a migraine attack, but they do tend not to sleep or eat properly, or they'll drink a lot of coffee to keep them going and that can bring on a migraine later." 
 
 It's enough to make you want to stay at work. So what can you do to reduce the risk of your holiday being ruined by an illness? "Take time to relax," says Shah. "Just travelling to get on holiday can be stressful in itself. When you arrive, you need to take it easy rather than going sight seeing straight away. Drink lots of water, have a massage. A lot of people take work with them. Don't do that - you're meant to be on holiday." 
 
 Vingerhoets found that the people who had suffered from "leisure sickness" in the past but who weren't affected by it now were those who reduced their workload or changed their attitude to work, and were attentive to signals that told them they needed to slow down. 
 
 Dr Sarah Brewer, a nutritionist and author of the Encyclopaedia of Vitamins, Minerals and Herbal Supplements, also thinks prevention is better than cure. "When I used to work in hospitals and would feel very stressed, I knew that when I had a break, I would come down with something for the first few days. Sometimes you just can't do anything about it." 
 
 Her advice is to do everything you can to manage your stress levels before you go on holiday and take exercise (but not competitive exercise, she points out). "Physical exercise resets the body's fight-or-flight reaction," she says. And, being a nutritionist, Brewer suggests boosting your immune system with nourishing foods and supplements. "Make sure you're getting a healthy diet with lots of fruit and vegetables, and omega-3 oils. I would recommend a multivitamin and mineral supplement with probiotics. I also like Siberian ginseng, which seems to help the body adapt to stress and - some research suggests - can help ward off colds. Vitamin C can help people under physical stress, though it can also help with mental stress, which depletes vitamin C levels as well. And a recent study published in The Lancet concluded that Echinacea can reduce the chances of catching a cold by 50%." 
 
 Brewer also advises reconsidering where you choose to take your holidays. "If you've been under a lot of stress, why fly a long way to the other side of the world? Your immunity will be depressed and you'll be exposed to bugs on the plane and foreign bugs when you get there. I recommend taking a holiday closer to home. Or what's wrong with relaxing at home, pottering around, doing some gardening and going for walks?"
– There’s a term for that cold you’re going to get when you take a few days off work this holiday season: leisure sickness. And, while there are no medical studies to confirm the phenomenon, a Dutch psychologist published findings in 2002 that 3% of 1,900 people polled did say they tended to get sick on weekends and vacations, Quartz reports. Professor Ad Vingerhoets of Tilburg University in the Netherlands previously told the Guardian that his own propensity for leisure sickness spurred him to conduct the study. His thoughts, and the reigning theory, hold that all the work stress leading up to a break compromises the immune system, and then once you're finally able to rest, all that stress catches up with you. But, as Quartz points out, becoming ill on vacation likely has more to do with traveling than with taking time off work. “Whether influenza, the common cold, or other viruses, it’s really quite clear that mass transportation contributes to transmission,” William Schaffner, professor of preventive medicine at Vanderbilt University Medical Center, tells Quartz. In our daily lives, we build up antibodies to fight the germs around us, but at an airport, we're exposed to new viruses from around the globe. Worse, many viruses spread more easily in crowded places like airports, and the relatively low humidity inside airplane cabins also help them to spread. There's also the fact that "people [probably] remember illnesses during vacations better than those that occur during more regular work schedules," one psychology professor points out. The best way to avoid getting sick this holiday season, Schaffner says: Get a flu shot. (This study predicts how often adults and kids will get the flu.)