Worried you'll soon be feeling under the weather now that the temperature's dropping? During cold and flu season, there's nothing like a coughing, sneezing coworker – or 12 – to get you washing your hands religiously and panicking about your health.

But maintaining good health isn't just about avoiding germs. With a strong immune system, you can fend off any viruses from the next cubicle over that may be floating your way – and these powerful foods can help build your defences.

1. Chaga mushroom
Chaga is a fungus that grows on birch and other hardwood trees, and looks more like burned charcoal than the typical mushroom you see at grocery stores. Filled with nutrients, chaga has a variety of uses in traditional Chinese medicine.

How it works: Chaga is packed with beta glucans, compounds that activate the production of antibodies. In a 2005 study, researchers from Seoul National University chemically suppressed the immune systems in mice and fed them chaga mushroom extract daily. Within eight days, the mice's immune systems had returned to normal.

How to take it: Chaga can be taken in capsule form or infused in tea. Chaga powder, which is relatively tasteless, can also be added to foods.

Where to find it: If you live near birch trees, you may have some in your backyard. If you decide to go on a chaga-hunting adventure, bring a guidebook to safely identify the mushrooms. Otherwise, you can buy chaga capsules or powder from health food stores. 

2. Garlic
On top of being delicious, garlic is filled with immunity-boosting compounds that help send germs packing.

How it works: When you chew or crush garlic, its enzymes combine to create allicin, a powerful antibiotic, antiviral and antifungal agent that also stimulates the immune system.

How to take it: Adding garlic to your favourite dishes is a great way to enjoy the health benefits. But if you want to stop an existing or oncoming cold in its tracks, slice a fresh clove into eight pieces and mix with a tablespoon of honey; swallow the mixture with the help of some water to relieve congestion and chest infections.

Where to find it: Garlic can be found in the produce aisle. Opt for fresh whole cloves rather than chopped or minced jar forms that contain preservatives.

3. Ginseng
You might have heard that ginseng can boost energy, but it's also beneficial for the immune system.

How it works: Studies have shown that on top of regulating immune cells, ginseng also helps control microbial infections. Plus, it's an adaptogen, meaning it helps our bodies cope with the physical effects of stress, which can have a negative impact on our immune systems.

How to take it: You can drink ginseng in a tea or take capsules.

Where to find it: Look for ginseng at health food stores and herbal dispensaries.

4. Turmeric
Ever wondered what gives curry powder its bright orange-yellow colour? It's turmeric, a powerful immunity booster.

How it works: Turmeric contains curcumin, a compound that increases the level of immunity-boosting proteins in our bodies. These proteins help fight bacteria and viruses when they try to attack. Turmeric is also a natural painkiller, an added benefit if you're actively fighting a flu virus.

How to take it: Turmeric is traditionally used in curries. You can also try sprinkling it on rice dishes, or even adding it to a smoothie. It also makes a great addition to a chai or spiced tea.

Where to find it: The spice aisle.

5. Ginger
On top of offering warming effects on a cool day, fresh ginger can also help you fight off infections.

How it works: Ginger promotes sweating, which detoxifies the body and can also help prevent illness. Scientists have discovered a protein called dermicidin that is manufactured in the sweat glands. When you sweat, dermicidin is transported to the surface of your skin, where it protects against invading germs.  

How to take it: Toss as much fresh ginger as you can handle in your morning smoothie, or boil a piece in water for a soothing ginger tea.

Where to find it: You can find fresh ginger in the produce aisle.

Meghan Telpner is a Toronto-based certified holistic nutritionist and author of the UnDiet: Eat Your Way to Vibrant Health.

If you do get sick during cold and flu season, try these 5 natural cold remedies.