Those loyalty cards in your wallet aren’t just taking up space — they might actually be encouraging you to spend more, Yahoo Canada’s recent “Talking Loyalty” research suggests.

On average, Canadians have four loyalty cards in their wallets and roughly 22 million consumers are members of at least one program, Yahoo reports, based on its survey research of 1,000 Canadians. More than half (56%) make a special effort to go stores where their loyalty cards can be used, and 47% say that having a loyalty card influences how much they spend. Millennials were also 5% more likely to spend more because they have a loyalty card, Yahoo says.

Market research firm Colloquy also recently found that retail loyalty programs are growing in Canada and that brands are tapping into customer data to tailor their program offerings.

So how can brands engage? Email has the greatest impact on loyalty program awareness, Yahoo says. That’s followed by display/native advertising and mobile apps, with millennials being nearly twice as likely as other demographics to prefer mobile for receiving loyalty information.