Subvisible

Subvisible is an adjective describing objects or phenomena not visible to the unaided eye, lying below the threshold of human vision. It is used across several disciplines to denote small or faint features that require magnification or instrumentation to observe.

In pharmaceutics and biopharmaceutical manufacturing, subvisible particles are particles roughly in the 0.1 to 100 micrometers size range that remain invisible to the naked eye. Their presence in injectable products matters because they can affect safety and efficacy, potentially triggering immune responses or infusion-related reactions. Regulatory guidance from pharmacopoeias and agencies specifies acceptable limits and analytical methods for detecting subvisible particles, including light obscuration and flow-imaging microscopy.

In environmental and atmospheric science, subvisible (or fine) particles refer to aerosols and particulates smaller than what is seen by the eye. These particles contribute to air quality, visibility reduction, and climate processes and are measured with instruments such as optical particle counters, cascade impactors, and gravimetric methods.

In materials science and formulation chemistry, subvisible particles can influence colloidal stability, suspension rheology, and product performance. Monitoring their size distribution and concentration aids in quality control and process optimization.

The term subvisible thus conveys both a quantitative sense (size below visibility threshold) and a qualitative sense (detection requires tools beyond ordinary sight). It is used primarily in technical contexts where particle size and visibility are critical factors.