From the outside, the differences between men and women are clear—muscle mass, height, reproductive organs, and body composition all set us apart. Yet, beneath the surface, more subtle variations exist, from how our brains process information to hormone concentrations, lung capacity, and even the structure of our airways. From the moment of conception, biological sex influences every tissue, organ, and bodily function, making it essential to approach disease prevention, diagnosis, and treatment in ways that reflect these differences.