The most surprisingly basic and everyday habits can influence how well your body fends off colds, flu and other infections, from not getting enough sleep to not keeping a pen in your bag.

Here’s a list of little things you may be doing (or not doing) that can make you sick.

Not Socializing Enough

Believe it or not, research shows that the fewer human connections we have at home, at work, and in the community, the likelier we are to get sick, have more anxiety, and live shorter lives. In one study, researchers who monitored 276 people between the ages of 18 and 55 found that those who had 6 or more connections were 4 times better at fighting off the viruses that cause colds than those with fewer friends.

What to do: Don’t let a jam-packed workday or hectic schedule get in the way of your friendships. Stop by a co-worker’s office for a quick Monday morning catch-up, or e-mail/text your friends at night to stay in touch when you’re too busy for phone calls.

Not Getting Enough Rest

The perfect example: college students who get sick after pulling all-nighters cramming for exams. Poor sleep is associated with lower immune system function and reduced numbers of killer cells that fight germs. In fact, University of Chicago researchers found that men who had slept only 4 hours a night for 1 week produced half the amount of flu-fighting antibodies in their blood (jump-started by a flu shot) compared with those who slept 7 1/2 to 8 1/2 hours.

What to do: Most adults need between 7 and 9 hours of uninterrupted rest every night, but how you feel in the morning and throughout the day may be a better gauge. If you’re tired when you wake up in the morning, you’re not getting enough—sleep, or maybe not enough quality sleep.

Being A Pessimist

Yes, your attitude affects your immune system too. Studies show that glass-half-empty types don’t live as long as those who look on the bright side. When pessimists put a more positive spin on the calamities in their lives, they have less stress and better health. A classic UCLA study found that law students who began their first semester optimistic about the experience had more helper T cells mid semester, which can amplify the immune response, and more powerful natural killer cells, than students who had a more pessimistic perspective. One reason could be that optimists take better care of themselves. It could also be due to less stress-related damage to the immune system, such as killer cells that suddenly become pacifists.

What to do: Try striking up a dinner table conversation with your family, where you all share a couple of good things that happened every day.

Taking Too Many Antibiotics

Taking antibiotics at the first sign of a sniffle can make you resistant to these drugs over time, causing more serious infections.

Researchers found that certain patients taking antibiotics had reduced levels of cytokines, the hormone messengers of the immune system. When your immune system is suppressed, you’re more likely to develop resistant bacteria or become sick in the future.

What to do: Take antibiotics only for bacterial infections, use them right away, and take the entire course. Don’t use antibiotics preventively unless prescribed by your doctor, and don’t save or share unfinished courses.

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