Heating pads are used to trigger reflex physical reactions that reduce pain, relax tight muscles, and control muscle spasms. Applying superficial heat to skin increases local blood flow which reduces stiffness, and it also stimulates thermoreceptors. Thermoreceptors are the body's temperature responders and they block pain transmitters before they reach the brain. There are several types of heating pads, including microwavable, chemical, water, and electric.
Microwaveable heating pads are generally made of flannel fabric and some type of grain such as rice, barley, buckwheat hulls, or wheat. These pads can be purchased in a store or made at home by sewing the fabric closed after inserting the grain. This makes them one of the most convenient options around. Simply place the filled heating bag in the microwave for one to three minutes and they're ready for use.
Chemical pads employ a substance such as sodium acetate that reacts when a piece of metal embedded in the supersaturated chemical is pressed. This initiates a crystallization process that results in instant heat. These pads can be reused by boiling the pad in water, then allowing it to reach room temperature again. This re-saturates the liquid and readies it for the crystallization process to begin when the metal piece is once again pressed.
Hot water bottles have been in use longer than any of the other options. These are made of rubber and have a stopper that allows hot water to be poured in and sealed. All types of fabric can be used to make hot water bottle covers, and even though electric and chemical heating pads have overtaken the top spots on the popularity lists, many are still opting for hot water bottles. They're one of the safest ways to apply heat, and users make cozy covers with knitted fabrics, fleece, and even faux fur.
Electric heating pads are a popular option. These devices are made of a sturdy material that houses an inner coil that heats up when the pad is plugged into an electrical outlet. They usually have a removable, washable fabric cover. The advantage of an electric device is its ability to produce a uniform amount of heat throughout the pad. The disadvantage is that they've been linked to burns and other injuries and must be used with care.
Only approved heating pads can be used by health care workers to treat patients. A special "medical use" designation is required due to accidental burns and injury to patients who are unable to sense the change in temperature, or unable to communicate that skin is becoming too hot. These devices must have more than one type of sensor to control the electrical output.