Stingray injuries are caused by the venomous tail spines or stingers of rays in the order Myliobatiformes, most significantly those belonging to the families Dasyatidae, Urotrygonidae, Urolophidae, and Potamotrygonidae. Stingrays generally do not attack aggressively or even actively defend themselves. When threatened, their primary reaction is to swim away. However, when attacked by predators or stepped on, the stinger in their tail is whipped up. This is normally ineffective against sharks, their main predator.
Depending on the size of the stingray, humans are usually stung in the lower limb region. Stings usually occur when swimmers or divers accidentally step on a stingray, but a human is less likely to be stung by simply brushing against the stinger. Surfers and those who enter waters with large populations of stingrays have learned to slide their feet through the sand rather than taking steps, as the rays detect this and swim away, as will stamping on the bottom as one treads through murky water. . There are reports of stingers breaking off in wounds, but this may be rare. This would not be fatal to the stingray as it will be regrown at a rate of about 1.25 to 2 centimetres (0.49 to 0.79 in) per month (though with significant variations depending on the size of the stingray and the exact species). Contact with the stinger causes local trauma (from the cut itself), pain, swelling, and muscle cramps from the venom, and possible later infection from bacteria or fungi. Immediate injuries to humans include, but are not limited to: poisoning, punctures, severed arteries and veins, and occasionally death.  Fatal stings are very rare, but can happen, infamously including Steve Irwin. In this case, the stinger penetrated the thoracic wall, causing massive trauma.
Biological structure of the barb
The barb is covered with rows of sharp flat spines, composed of vasodentin. Vasodentin is an incredibly strong cartilaginous material which can easily cut through flesh. The undersides of the spines contain two longitudinal grooves which run along the length of the spine and enclose venom-secreting cells. Both the venom-secreting tissues and vasodentin are enveloped in an epidermis that tears open when the barb is plunged into a victim. Some spines may break off as the barb exits the wound and stay within the victim causing prolonged envenoming.
Many victims of stingray related injuries suffer from physical effects including nausea, vomiting, diarrhea, extreme pain at the wound, muscle cramps, and a laceration at the puncture site. There have been cases of severe consequences which may include embedded spines, infection, hypotension, and even possible amputations or death. Stingray wounds have also been found to bleed profusely and for a long amount of time after the initial puncture. It has been suggested that there may be some sort of anti-hemoglobin agent incorporated with the secreted venom, but James H. Diaz of Louisiana State University has refuted that theory.
Treatment for stings may include application of hot water (optimum temperature is 45 °C (113 °F), taking care not to cause burns), which can help ease pain. Pain relief with hot water has been well documented in multiple observational studies and 1 small experimental study. However, multiple theories as to the mechanism of pain relief from hot water have been suggested. A popular theory that hot water denatures the stingray venom has been questioned because the temperatures required would need to penetrate deeply into the puncture wound and would likely cause thermal damage to surrounding tissue. Other proposed mechanisms include modulation of pain receptors in the nervous system through mechanism such as the gate control theory and the diffuse noxious inhibitory control theory. Antibiotics may be administered to prevent infection if there is a delay in treatment, if the wound is deep, or if there is a large amount of foreign material in the wound. Immediate injection of a local anesthetic in and around the wound, or a regional nerve blockade, can be helpful, as can the use of parenteral opiates such as intramuscular pethidine. Local anesthetic may bring almost instant relief for several hours. Vinegar and papain are ineffective. Pain normally lasts up to 48 hours, but is most severe in the first 30–60 minutes and may be accompanied by nausea, fatigue, spreading cramps, headaches, fever, and chills. All stingray injuries should be medically assessed; the wound must be thoroughly cleaned, and surgical exploration is often required to remove any barb fragments remaining in the wound. Following cleaning, an ultrasound is helpful to confirm removal of all the barb fragments. Not all remnants are radio-opaque; x-ray radiography imaging may be helpful where ultrasound is not available.
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People who step on a stingray most frequently are injured on their feet and lower legs.
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