susceptibil

Susceptibility, sometimes encountered as susceptibil in some languages, is a general term that describes the propensity of a system to undergo a change in response when exposed to an external influence. The concept is used across disciplines, including physics, materials science, and biology, to describe how readily a material, organism, or environment reacts to a stimulus such as a magnetic or electric field, or a pathogen.

In physics, magnetic susceptibility χm quantifies how much magnetization a material develops in response to an applied magnetic field, with M = χm H in isotropic cases. χm can be positive (paramagnetic) or negative (diamagnetic). In dielectrics, electric or dielectric susceptibility χe relates polarization P to an electric field E via P = ε0 χe E, and the relative permittivity εr equals 1 + χe. Susceptibility is scalar for isotropic media and a tensor for anisotropic materials, and it is dimensionless.

In biology and epidemiology, host susceptibility denotes the inherent or acquired likelihood that an individual will become infected after exposure to a pathogen. Factors include genetics, immune status, age, nutrition, prior exposure, and vaccination. Population-level susceptibility influences the spread of disease and is estimated using measures such as relative risk or odds ratios. Susceptibility is distinct from immunity and can be modified by vaccination, treatment, or changes in behavior.

The term derives from Latin susceptibilis, meaning able to be touched or affected. Beyond magnets and health, susceptibility appears in materials science, geophysics, and social sciences to describe vulnerability to stimuli such as stress, corrosion, or information.