Why were mesmerism and phrenology considered pseudoscientific medical doctrines?

Mesmerism and phrenology are classified as pseudoscientific medical doctrines because they relied on speculative theories that lacked empirical evidence and failed to withstand rigorous scientific scrutiny.123

Mesmerism

Developed by Franz Anton Mesmer, this system posited that an invisible fluid, which he termed "animal magnetism," flowed through the body and influenced health. Mesmer claimed that disease resulted from obstacles in this fluid's flow, which could be corrected by trained practitioners. In 1784, a commission including Benjamin Franklin and Antoine-Laurent Lavoisier investigated these claims and concluded that Mesmer could not support his scientific assertions. While the practice likely provided some relief through the power of suggestion—a precursor to modern hypnotism—the underlying theory of a magnetic fluid was scientifically baseless.23

Phrenology

Propounded by Franz Joseph Gall, phrenology held that specific mental faculties were located in distinct regions of the brain and that the size of these regions could be determined by examining the contours of the skull. This doctrine was based on specious grounds, such as mapping traits like "theft" or "murder" onto the head based on arbitrary observations of individuals in jails and asylums. Although popular for a time, phrenology has been entirely discredited by modern scientific research.13