Injury is physiological damage to the living tissue of any organism, whether in humans, in other animals, or in plants.
Injuries can be caused in many ways, including mechanically with penetration by sharp objects such as teeth or with blunt objects, by heat or cold, or by venoms and biotoxins. Injury prompts an inflammatory response in many taxa of animals; this prompts wound healing. In both plants and animals, substances are often released to help to occlude the wound, limiting loss of fluids and the entry of pathogens such as bacteria. Many organisms secrete antimicrobial chemicals which limit wound infection; in addition, animals have a variety of immune responses for the same purpose. Both plants and animals have regrowth mechanisms which may result in complete or partial healing over the injury. Cells too can repair damage to a certain degree.
Injury in animals is sometimes defined as mechanical damage to anatomical structure,[1] but it has a wider connotation of physical damage with any cause, including drowning, burns, and poisoning.[2] Such damage may result from attempted predation, territorial fights, falls, and abiotic factors.[2]
Injury prompts an inflammatory response in animals of many different phyla;[3] this prompts coagulation of the blood or body fluid,[4] followed by wound healing, which may be rapid, as in the cnidaria.[3] Arthropods are able to repair injuries to the cuticle that forms their exoskeleton to some extent.[5]
Animals in several phyla, including annelids, arthropods, cnidaria, molluscs, nematodes, and vertebrates are able to produce antimicrobial peptides to fight off infection following an injury.[1]
Injury in humans has been studied extensively for its importance in medicine. Much of medical practice, including emergency medicine and pain management, is dedicated to the treatment of injuries.[6][7] The World Health Organization has developed a classification of injuries in humans by categories including mechanism, objects/substances producing injury, place of occurrence, activity when injured and the role of human intent.[8] In addition to physical harm, injuries can cause psychological harm, including post-traumatic stress disorder.[9]
In plants, injuries result from the eating of plant parts by herbivorous animals including insects and mammals,[10] from damage to tissues by plant pathogens such as bacteria and fungi, which may gain entry after herbivore damage or in other ways,[11] and from abiotic factors such as heat,[12] freezing,[13] flooding,[14] lightning,[15] and pollutants[16] such as ozone.[17] Plants respond to injury by signalling that damage has occurred,[18] by secreting materials to seal off the damaged area,[19] by producing antimicrobial chemicals,[20][21] and in woody plants by regrowing over wounds.[22][23][24]
Cell injury is a variety of changes of stress that a cell suffers due to external as well as internal environmental changes. Amongst other causes, this can be due to physical, chemical, infectious, biological, nutritional or immunological factors. Cell damage can be reversible or irreversible. Depending on the extent of injury, the cellular response may be adaptive and where possible, homeostasis is restored.[25] Cell death occurs when the severity of the injury exceeds the cell's ability to repair itself.[26] Cell death is relative to both the length of exposure to a harmful stimulus and the severity of the damage caused.[25]
Injuries can be categorized based on the type of harmful agent or force that impacts an organism, leading to varying forms of damage.
Physical Injuries are among the most common and occur when external mechanical forces cause damage to the body.[27] These injuries can range from superficial wounds like cuts and bruises to more severe conditions such as bone fractures and joint dislocations. Sprains and strains are also common types of physical injuries, affecting ligaments and muscles, respectively. Physical injuries often result from accidents, sports, or violent impacts, and their severity can vary widely, from mild discomfort to life-threatening trauma requiring surgical intervention.
Chemical Injuries occur when the body comes into contact with harmful substances, such as acids, alkalis, or poisons. These injuries can cause chemical burns, irritation, or systemic toxicity, depending on the chemical and the duration of exposure. For instance, acid burns can lead to severe tissue damage and scarring, while inhaling toxic fumes may harm internal organs like the lungs.[28] Chemical injuries are often seen in industrial accidents, improper handling of household products, or deliberate poisoning and require immediate medical attention to prevent long-term damage.
Thermal Injuries result from exposure to extreme temperatures, either heat or cold. Thermal burns, caused by contact with fire, hot surfaces, or scalding liquids, are a common form of thermal injury. On the opposite spectrum, frostbite occurs when tissues freeze due to prolonged exposure to freezing temperatures, leading to tissue damage or necrosis.[29] The severity of thermal injuries is often classified by the depth and extent of the damage, with severe cases requiring surgical interventions like grafting or even amputation.
Electrical Injuries happen when an electrical current passes through the body, potentially causing burns, nerve damage, or even cardiac arrest. These injuries can result from accidents involving electrical appliances, power lines, or lightning strikes.[30] The extent of the damage depends on factors such as the voltage, duration of contact, and the path the current takes through the body. Electrical injuries are particularly dangerous because they often cause internal damage that is not immediately visible, making prompt medical evaluation crucial.
Radiation Injuries are caused by exposure to various forms of radiation, including ultraviolet (UV) rays, X-rays, or ionizing radiation from nuclear sources. Sunburn is a common example of UV-induced radiation injury, while prolonged exposure to X-rays can lead to radiation burns or increase the risk of cancer.[31] Severe radiation injuries, such as those caused by nuclear accidents, can result in acute radiation syndrome, which affects multiple organ systems and can be fatal. Protective measures, like shielding and limiting exposure time, are essential to reduce the risk of these injuries.
Biological Injuries arise from interactions with living organisms, such as bacteria, viruses, or venomous animals.[32] Infections caused by bacterial or viral pathogens can lead to localized or systemic damage, as seen in abscesses or sepsis. Bites and stings from animals, such as snakes, spiders, or insects, can inject venom that disrupts blood clotting, damages tissues, or causes severe allergic reactions. These injuries often require specific treatments, such as antibiotics for infections or antivenoms for envenomation, to mitigate their effects.