Taking probiotic supplements to reinstate the balance between good and bad bacteria, which coexist in the gut, and improve health is increasing in popularity. So much so that an estimated $2.5 billion was spent on probiotics supplements in 2018. About $10 billion was spent on foods and drinks that contain the living microorganisms.

With sales booming, most people would think there must be a lot of scientific evidence behind the benefits of probiotics. However, this is not exactly the case. A lot of research, while promising, is still being done. But many studies have small sample sizes and lack follow-up data.

Probiotics work by decreasing the number of harmful bacteria in the intestines. They are mostly taken to improve digestion, but some research suggests they may also be helpful in treating skin conditions like eczema and even seasonal allergies.

Just as there are many different bacteria in a person’s gastrointestinal microbiota, there are many different type of probiotics, each with its own effect on the body. This is also what makes taking the right dosage tricky.

To determine everything you need to know about probiotics, 24/7 Wall St. consulted a doctor specializing in internal medicine and a certified clinical nutritionist, and reviewed scores of studies and meta-analyses published in medical journals about the benefits and side effects of probiotic supplements.

Click here to read about everything you need to know about taking probiotics.