Cold helps cut down on swelling by shrinking the blood vessels. This
reduces bleeding and therefore swelling in the affected area. Cold also
helps keep the muscles from spasming (contracting uncontrollably) and relieves
pain. But too much cold can damage the skin, which is why you should apply
ice for a while, take a break, then apply it again. This allows the skin
to return to normal temperature between treatments.
Generally speaking, you should apply ice for 10 to 30 minutes, depending
on the body part and your own comfort level. Areas with little body fat
(like the ankle, knee, and elbow) cannot handle cold as well as fatty areas
(like the thigh and buttocks). A bag of frozen peas can make an excellent
substitute for an ice bag, since the peas will better mold to the shape
of your ankle (or knee or whatever).
Cold gel packs that can be frozen and refrozen cool the skin faster than
an ordinary ice bag and should only be applied for short periods. Chemical
cold bags (which stay at room temperature until squeezing mixes the chemicals
inside) don't get as cold as an icebag, and can stay on the skin for longer
periods of time. Cold therapy may not be recommended for people who are
very sensitive to cold, those with blood vessels too near the skin, and
diabetics and others who have problems with diminished blood flow. If you're
one of those people, you should talk to your doctor about applying ice to
Heat can also relax muscles and relieve pain, but it makes swelling worse
by stimulating blood flow. That's why cold is best immediately following
an injury and for at least 48 hours afterward, or until the swelling goes
down. Then heat can help, as the increased blood flow "cleans"
out the damaged area.