Recent years have witnessed a growing number of online platforms disclosing the historical prices of products to consumers. While such transparency is typically viewed as consumer-friendly, this paper shows that it can raise prices and reduce consumer welfare. We develop a dynamic model in which a seller faces sequential consumers who are uncertain about product quality and rely on past consumer reviews. A positive review can result either from high product quality or from a low price. When historical prices are not disclosed, future buyers cannot distinguish between these possibilities, giving the seller an opportunistic incentive to underprice initially to boost perceived quality. When historical prices are disclosed, consumers interpret reviews in context, eliminating the seller’s incentive to discount early. As a result, price transparency removes introductory discounts and drives up prices—benefiting the seller and the platform, but potentially hurting consumers. Our findings challenge the common belief that more information disclosure always benefits buyers and highlight the strategic role of price history in shaping consumer learning and seller behavior. The results offer actionable insights for platform designers and regulators, suggesting that well-intentioned transparency policies may have unintended consequences for market outcomes.