Toxicologists have long held that the dose makes the poison: A substance can cause harm only in amounts high enough to overwhelm the body’s defenses. But a major conceptual shift is underway, a leading expert said recently at AAAS, with much more attention being paid to low-dose chemical exposures and the impact they can have even many years later.

A recent AAAS seminar explored the potential consequences of direct-to-consumer genetic testing—and the appropriate role of government regulation—through the lens of two individuals who went through genetic testing.