Pain is an unpleasant sensation and emotional experience associated with actual or potential tissue damage. Pain, as unpleasant as it is, is a vital mechanism in evolution, to enhance the chances of survival. As a warning signal, it causes animals to change their movement pattern, e.g. by walking on only three legs to allow the injured fourth to heal.  

Based on the origin, pain can be classified in nociceptive, neuropathic and psychogenic.

Nociceptive pain is formed when thermal (e.g. heat or cold), mechanical (e.g. crushing, tearing, shearing, etc.), chemical (e.g. iodine in a cut or chemicals released during inflammation) or biological (e.g. diseases) stimuli of harmful intensity affect tissues. It can affect skin, muscles, joints, connective tissue, bones, but also internal organs. It is triggered by incidents such as injuries, burns, bruises, bone fractures or diseases of internal organs (e.g. abdominal pain). Pain in the skin, muscles, joints and connective tissue is usually easy to diagnose. Nociceptive pain usually disappears as soon as the cause has been eliminated (e.g. the burn has healed). Internal organ or deep tissue pain is more difficult to detect in animals, and this is where paying attention to your pet’s body language is essential.

Neuropathic pain is caused by damage or disease affecting any part of the nervous system involved in bodily feelings. Bumping the "funny bone" in the elbow elicits acute neuropathic pain, for example.

Psychogenic pain is caused, increased, or prolonged by mental, emotional, or behavioral factors, and should also be taken into consideration when diagnosing the causes of pain in animals.

Pain can occur suddenly (e.g. a dog steps onto a piece of broken glass and cuts its paw, a cat jumps onto a hot plate and burns its paws). The pain disappears gradually after removal of the harmful stimulus. In this case the pain was acute. However, pain can also be chronic and last for a long time, such as for instance, in arthritis, a painful joint disease caused by long-term wear and tear of joints. Chronic diseases can severely reduce an animal's quality of life if left untreated.

Lawmakers and veterinarians have long recognized that pain in pets must be taken seriously. Animal protection laws in some countries stipulate that animals must be spared unnecessary pain, and veterinarians are obligated to protect them accordingly.  

As a responsible animal owner, it is necessary to do everything possible to prevent animals from experiencing (prolonged) pain, and to act immediately when signs of pain are detected.