According to the Harvard School of Public Health, more research is needed to determine whether collagen supplements can help humans grow new collagen, which diminishes as we age. And as The New York Times reports, while some studies have indicated that taking collagen for several months might improve skin elasticity, those studies were small and received their funding from collagen supplement manufacturers.

Greens powders—which usually contain some combination of dried and ground leafy greens and seaweeds, grasses, probiotics, and herbs—fare somewhat better under scrutiny, but experts still encourage skepticism. According to WebMD, greens powders can be useful to supplement a healthy diet with additional vitamins and antioxidants. One study linked greens powders with improvements in blood pressure. But greens powders are not equivalent to whole foods—some nutritional content, such as fiber, is lost during processing, and overconsumption of some vitamins can be harmful.

Another thing for consumers to consider: The supplement market is largely unregulated, and poor-quality products with inaccurate labels are common. In an interview with The Cut, Evan Reister, a Doctor of Nutrition Science at American University, advises consumers to look for brands that are USP or NSF certified. These certifications require manufacturers to label their products accurately and submit them to third-party lab testing for certain contaminants.