SIGNIFICANCE: Past studies show rising mortality and morbidity among middle-aged white Americans since the 21st century. This research analyses trends in declining self-rated health (SRH) across demographic groups, focusing on shifts in SRH inequalities by gender, race, and socioeconomic status (SES). It sheds light on declining health trends in the United States and deepens our understanding of health inequalities and their dynamics in high-income countries. METHOD: We analyse 29 waves of cross-sectional data from the General Social Survey (1972-2018, N = 46,133) using Bayesian Hierarchical Age-Period-Cohort Cross-Classified Random Effect models (BHAPC-CCRM) to estimate age, period, and cohort effects, and changes in health gaps over time as interactions between period and race, gender, or SES. RESULTS: SRH improved until the 21st century but then declined across all gender, race, income, education, and employment groups after controlling for age and cohort effects. The racial health gap has continued since 2000, with a slight erosion of white health privilege. Nonwhite, low-income, non-college-educated, unemployed, and unmarried individuals have seen further declines in SRH. Baby Boomers' health advantage was wiped out after 2000. INTERPRETATION: In line with the health reversal literature in the U.S. and the U.K., SRH has deteriorated in the 21st century for all racial, gender, and SES groups in the U.S. The diminishing SRH advantage for whites results from a faster decline compared to Blacks and other non-white groups. However, significant racial and SES disparities in SRH persist, with disadvantaged groups experiencing poorer SRH. We discuss the policy implications.