Even before the microbiome craze — the hope that the bacteria in your gut holds the key to good health — people were ingesting cultures of living micro-organisms to treat a host of conditions. These probiotics have become so popular that they’re being marketed in foods, capsules and even beauty products.

Probiotics have the potential to improve health, including by displacing potentially harmful bugs. The trouble is that the proven benefits involve a very small number of conditions, and probiotics are regulated less tightly than drugs. They don’t need to be proved effective to be marketed, and the quality control can be lax.

In a recent article in JAMA Internal Medicine, Pieter Cohen, an associate professor of medicine at Harvard Medical School, urges us to consider the harms as well as the benefits. Among immune-compromised individuals, for instance, probiotics can lead to infections.

Consumers can’t always count on what they’re getting. From 2016 to 2017, the Food and Drug Administration inspected more than 650 facilities that produce dietary supplements, and determined that more than 50 percent of them had violations. These included issues with the purity, strength and even the identity of the promised product.