The Mayo Clinic defines probiotics as good bacteria that are either the same as or very similar to the bacteria that are already in your body. Your lower digestive tract alone teems with a complex and diverse community of these bacteria. And these probiotics have a positive effect on your gut's microbiome as well as your immune system.

According to the University of Washington's Center for Ecogenetics and Environmental Health, your microbiome is the genetic material of all the microbes and microorganisms—bacteria, fungi, protozoa and viruses—that live on and inside the human body. Not generally recognized to exist until the late 1990s, it is essential for human development, immunity and nutrition.

The more the merrier, right? Because they help combat harmful bacteria, it's a good idea to incorporate them into your diet. Plus, as Vincent Pedre, M.D., medical director of Pedre Integrative Health and author of Happy Gut, explains, many aspects of the modern lifestyle—from the emergence of antibiotics and the use of pesticides in our food to the near-constant presence of stress—effect the microbiome and chip away at our gut's barrier of good bacteria.

Here's where things get interesting. Because according to recent studies by the National Institutes of Health's Human Microbiome Project, your gut's microbiome influences the overall health of your entire body. In a recent study published in Nutrients, researchers investigated probiotics' immune-boosting powers in yogurt. They found that the live bacteria interact with the microbes in our intestines to produce such vitamins as B6, B12 and K; while helping ward off bad bacteria such as E. coli and Salmonella. This, in addition to keeping the bowels moving efficiently. Probiotics may also enforce our intestines' natural barrier function, helping to keep viruses like the flu and common cold from getting through. And because they're such potent anti-inflammatories, probiotics have been shown to help clear up skin, reduce allergic reactions, as well as improve cholesterol levels and glucose metabolism.

The good news is that while there are many strains, the most effective and potent, lactobacillus acidophilus (l. acidophilus) and/or Bifidobacterium (B. bifidum), are fairly common and easy to incorporate into your daily routine. Either in the form of supplements (powders, pills or chewy chocolates or gummies) or food that's naturally rich in probiotics (yogurt, pickles and kimchi). Herewith, a few of our favorites.