For decades the technique of “sweating a leg” has been a mainstay in conservative management of equine leg injuries, as well as improving cosmetic appearance in certain situations. While topical medications and application techniques vary greatly, all sweats have three common ingredients:
- A topical medication consisting of a base (traditionally nitrofurazone, or Fura-Zone, ointment) often mixed with various additives, most commonly an anti-inflammatory (a steroid such as dexamethasone or a non-steroidal anti-inflammatory such as diclofenac), and dimethyl sulfoxide (DMSO) as a carrying agent.
- Plastic wrap.
- A firmly applied stable bandage.
The purpose of a sweat is to apply moist heat and compression to a structure to increase the tissue temperature, stimulate circulation, and aid in the removal of edema (fluid swelling). Edema occurs when the fluid that naturally leaks from blood vessels is not effectively carried away by the lymphatic system, due to poor circulation or conditions in which excess fluid leakage overcomes normal lymphatic return capacity. The nitrofurazone (or other base ingredient) creates a moist environment, while the DMSO stimulates blood flow and helps carry any other medications in the mixture into the tissues. Saran or other plastic wrap helps keep the area moist and warm, while the stable bandage helps further retain heat and compresses the swollen tissues to help the lymphatic system clear up excess extracellular fluid.
Sweating is best used once the acute stage of inflammation has resolved, since you do not want to add further heat to freshly damaged tissue. Ice and cooling clay poultices are more appropriate choices in those initial stages. Once things have settled down and healing has begun, you can use a sweat to reduce edema, encourage circulation, and aid absorption of topical medication. Ask your veterinarian when it’s appropriate to start sweating—usually when there’s no obvious heat in the affected limb.
Sweats are also useful for managing old injuries that have resulted in stiffened tissues, such as an old suspensory ligament injury with scarring or the thickened capsule of an arthritic joint. Keeping those areas warm and supple can prevent repeat injury and help a horse feel more comfortable, particularly at the start of exercise when core and tissue temperatures are still below optimal for maximum function and flexibility.
In cases when an area is not easy to bandage, you can replace the plastic wrap and stable bandage with a neoprene boot shaped to fit the area being sweated, such as a hock or knee. Neoprene wraps are also used to sweat and reduce the throatlatch area in conformation horses to give it a cleaner appearance. When using neoprene we typically skip the DMSO because it can create excess heat to the point of skin irritation. If DMSO is an ingredient in your sweat, be sure the leg is completely dry before application because when DMSO mixes with water, a significant exothermic (heat-releasing) reaction can occur to the detriment of skin health. Also avoid using DMSO on scrapes or skin injuries.
Some horses with very sensitive skin, particularly nonpigmented limbs, can be sweated effectively with just a little rubbing alcohol, plastic wrap, and a bandage. With extremely sensitive horses, place the plastic wrap over the cotton (or pillow wrap or no-bow) so it’s not directly against the skin. Nitrofurazone-based sweats will stain the skin and hair yellow, so an alcohol-based sweat might be a better choice if you’re headed for the show ring.
Sweats are typically applied on a 12-hours-on, 12-hours-off schedule; however, your veterinarian might have different instructions depending on your horse’s situation. Most veterinarians make a medicated sweat for these purposes and can give you specific instructions on safe use and medication withdrawal time. Remember to wear gloves when applying a sweat to protect yourself, particularly if DMSO is an ingredient.