 What about chlorella, sold as a dietary supplement? Harmful? Harmless or helpful? There was a report in the journal Veterinary Pathology of a golden retriever killed by chlorella. It invaded her body and started eating its way up to her brain. This is showing the algae creep up her spinal cord. But this is only if you dip an open wound into a scummy pond or something. The chlorella that's in the health food store is dried and dead. There have been reports of adverse reactions, for example, here in 11-year-old hospitalized for kidney failure, which went away when he stopped chlorella. But this was thought to be an allergic reaction. Similarly, there are reports of sun-sensitive rashes and asthma triggered by breathing and stuff in. But again, they don't appear to be caused by a toxin, like you might find in blue-green algae supplements or spirulina, but just more like rare reactions in sensitive individuals. For the vast majority of people, chlorella can be considered helpful. Packed with lots of nutrients, like tiny little dark green leafies, kind of taste like you're drinking your lawn, though, and kale is cheaper.