Big brands would rather shoppers not ask Alexa.

The growing popularity of voice-search assistants poses a threat to the biggest makers of household staples. Already grappling with upstart rivals, changing consumer tastes and the rise of e-commerce, personal-care and packaged-foods makers have yet to figure out how to leverage the technology.

Unlike in stores or online, where an array of brands get plenty of exposure, voice-search assistants like Amazon.com Inc.’s Alexa often steer shoppers to a single product, usually selected by an algorithm with no input from the sellers. That isn’t a big problem now, as voice searches account for a sliver of purchases. But it could be.

In the next five years, half of searches on the web will be done via voice, estimates Sebastien Szczepaniak, a former Amazon executive who now heads e-commerce for Nestlé SA, the world’s biggest packaged-foods company. Consulting firm Capgemini says voice-assistant users will spend 18% of their total expenses via voice assistants in the next three years, up from 3% currently.

This story originally appeared in The Wall Street Journal.