You're at increased risk for colds and the flu over the holidays, but a few simple measures will help lower your chances of getting sick, an expert says.

"With all the hustle and bustle of the holidays, we come into contact with more germs, and even sugary treats, that can weaken the immune system," Stacey Gorski, an assistant professor of biology and an immunology specialist at University of the Sciences in Philadelphia, said in a university news release.

Your first line of defense is a flu shot. The flu causes an average of 30,000 deaths and more than 200,000 hospitalizations every year, Gorski said.

You need to keep exercising over the holidays, because physical activity helps keep your immune system primed for action, she noted.

Getting enough sleep also keeps your immune system strong, she said.

It may be difficult, but you should limit holiday sweets because high sugar levels can weaken your immune system. Do not eat raw cookie dough, which can cause E. coli or salmonella infections, Gorski added.

It's also important to stay warm. Research in mice found that just a slight drop in temperature significantly increased their susceptibility to the cold virus. Having a humidifier can also help. Lower humidity levels make it easier for viruses and bacteria to spread between people, Gorski said.