These days, the promotions come directly, and often custom tailored, to you. But at what cost?

The lure of relevant deals is conditioning us to give up our personal information, said Joseph Turow, a professor at the Annenberg School for Communication at the University of Pennsylvania who studies marketing and digital privacy. “This is such a habit-forming activity that you begin to say, ‘Well, if I do it for shopping, I’ll do it for the government,’” he said.

He warned that it’s teaching you “that giving up your data is just a part of life.”

How do promotions get to you ? On email, text, social media and the web, promotions are lurking everywhere. People may go online or on apps to find deals, or get recommendations based on their history as they browse a store with its app open on their smartphones.

Or people may be quietly, specifically targeted. “Some deals might get to us because a company that’s interested in promoting a certain type of thing has bought information about us from a data broker,” said Laura Moy, the executive director of the Center on Privacy and Technology at Georgetown Law School.

But many trade-offs are more transparent: you give us something, we’ll give you something. From the moment you log on to the site of Outdoor Voices, an athleisure brand, it touts an “exclusive birthday offer” in exchange for your email address.

Revolve Clothing offers 10 percent off for subscribing to its newsletter. Baggu, which makes those nylon bags beloved by Aidy Bryant, gives free shipping in the United States on orders over $30. According to Honey, the number of carts an average member finds a coupon for each year has increased 33 percent.