Being female is expensive. And not just because the average woman spends roughly $15,000 on makeup in her lifetime—even when women buy the exact same products that men do, female shoppers end up spending more.

An investigation by The Times of London found that Britain’s biggest retailers—including Tesco, Boots, and Amazon—are charging British women an average 37% more than men for items that are essentially identical. This follows a similar study released last month by the New York City Department of Consumer Affairs, which found that, on average, women in the U.S. pay 7% more than men for equivalent products.

Just how large that pricing disparity is depends on the product in question. The Times, for instance, found that a pair of women’s Levi’s 501 jeans are an average 46% more expensive than the men’s version—even when they have the identical waist size and leg length. In the U.S., personal care products had the greatest gender-pricing gap, with women’s items—like the infamous pink razor—costing 13% more than men’s. Women’s clothing cost an average of 8% more than clothing for men, though the difference varied dramatically depending on the retailer: A Forbes analysis of individual retailers in the U.S. found that Club Monaco charges 28.9% more for women’s clothing than men’s; at Urban Outfitters the disparity is 24.6% and at H&M 7.9%.

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Some would argue that the “pink tax” is simply the result of women’s market preferences. In, a blog affiliated with the monthly libertarian magazine Reason, staff editor Elizabeth Nolan Brown notes:

While the pink razors with the butterflies on the packaging my be marketed toward women, no one’s forcing us to buy those over basic blue Bics. If the products in this study really were identical save for some totally non-desired factors, it seems likely that women, or at least a larger proportion of women, would simply choose the products marketed toward men.

Yet saying that women can choose to buy men’s products is like saying women can choose not to wear makeup: a logical, yet often impractical idea, given the emphasis that our society puts on women’s appearances and the sheer magnitude of the women-focused marketing machine.

As economics professor Daniel Hamermesh noted to the New York Times last year, “I think we’d be a fairer world if beauty were not rewarded, but it is.”