A noxious stimulus is "an actually or potentially tissue damaging event." It is a prerequisite for nociception

Nociception

Nociception is defined as "the neural processes of encoding and processing noxious stimuli." It is the afferent activity produced in the peripheral and central nervous system by stimuli that have the potential to damage tissue...

, which itself is a prerequisite for nociceptive pain

Noxious stimuli can either be mechanical

Mechanics

Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....

 (e.g. pinching or other tissue deformation), chemical (e.g. exposure to acid

Acid

An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

 or irritant

Irritation

Irritation or exacerbation, in biology and physiology, is a state of inflammation or painful reaction to allergy or cell-lining damage. A stimulus or agent which induces the state of irritation is an irritant...

), or thermal

Thermal

A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...

 (e.g. high or low temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

s).

There are some types of tissue damage that are not detected by any sensory receptors, and thus cannot cause pain. Therefore, not all noxious stimuli are adequate stimuli of nociceptors. The adequate stimuli of nociceptors are termed nociceptive stimuli. A nociceptive stimulus is defined as "an actually or potentially tissue damaging event transduced and encoded by nociceptors."