When you bruise your arm, twist your ankle or suffer a similar minor injury, many doctors recommend a simple, four-step self-care procedure known by the acronym RICE.

"Rest, ice, compression, elevation," explains sport physician Axel Klein, vice president of the German Society for Sport Medicine and Prevention (DGSP). These steps help to reduce swelling and ease the pain.

Swelling can result from damage to small blood vessels, causing them to leak and blood to pool, and the body's inflammatory response meant to remove components of damaged tissue. Blood vessels in the area dilate and blood flow into the tissue increases, as does blood vessel permeability, allowing fluid, proteins and white blood cells to migrate to the site of the damage.

Applying a cold wrap to the injured area reduces swelling by constricting the blood vessels and slowing the flow of blood. The cold also eases pain by inhibiting nerve conduction – including pain signals to the brain – thereby making the area feel numb.

Compressing the area by wrapping it in an elastic bandage helps to reduce swelling as well, and raising it above the level of your heart reduces throbbing along with swelling and pain.

Orthopedic and trauma surgeon Dr. Thomas Gottfried recommends applying cold to all acute injuries, including contusions and fractures, but never to open wounds. To prevent frostbite, doctors say it's important not to ice the area for more than 20 minutes at a time.

"There are two bodily reactions to cold that can be felt," points out Gottfried, explaining that the initial "pain" upon application of cold is normal and no cause for worry. "Then comes habituation to the cold, followed by the second sensation of pain. You need to be alert to it and then stop the application of cold to prevent frostbite."

"You can intermittently rub an ice cube over the injured area," suggests Klein, which is safe. This doesn't expose the skin to continuous cold, but provides a repeated analgesic effect, he says.

Klein recommends applying cold to an injured area at spaced intervals for no longer than two days. "From the third day on, at the latest, it's better to stimulate metabolism again so that the tissue is well supplied with blood," he says. Cold slows metabolism.

If you follow these guidelines, you can safely ice a minor injury at home without medical supervision – with a few caveats.

"You need to be careful if you have certain conditions, for example, a circulatory problem or sensitiveness to cold," notes Gottfried. The same goes for sensory disorders in which the body's warning mechanisms don't function properly, since "affected persons often don't feel pain caused by cold."

The application of heat – in the form of a cherry pit pillow, hot-water bottle or infrared lamp, for instance – can alleviate the symptoms of minor injuries too, though not acute ones.

"Heat makes the tissue more supple," Gottfried says, noting that it helps to relieve strains, such as extreme muscle soreness after a workout. "It's also effective for adhesions or scarring, and can be helpful in all cases of connective tissue changes."

Heat dilates blood vessels, thereby increasing blood flow. It has a pain-reducing effect as well, which is why it's used, for example, to alleviate menstrual cramps and chronic inflammation.

The appearance of red blotches on the skin after the application of heat is generally no cause for alarm. If they're accompanied by pain, however, they may be a sign of first-degree burns, warns Gottfried. While such burns leave no lasting damage, the combination of redness and pain should always be seen as a warning sign, he says.