Sweating is a normal physiological phenomenon when horses exercise aiding blood circulation and that leads to increased body temperature. Perspiration is therefore a cooling process that helps lower the body temperature. However, if a horse sweats profusely or is unable to sweat, it may suggest that the horse is not in good health, or suffering from a disease.

In a racing commentators' opinion, horses that types of sweating which occur on the training track or prior to races can be roughly classified into four conditions: normal perspiration; heavy sweating owing to excess condition; abnormal perspiration due to weakness of constitution; nervous sweating. "Normal perspiration" aside, it is not encouraging to see the other types of sweating mentioned. Excessive perspiration can cause fatigue such that horses fail to perform satisfactorily in races. Exceptions occur of course as each horse has its own characteristics.

Normally, horses sweat if they are not fit, especially when resuming training after a summer break. Since horses experience much less exercised during the break, fat is stored in their bodies and they may become a little flabby. In early season, it is common to see that some horses perspire all over in morning workouts, particularly on the neck, chest and shoulders. Heavy sweating often works itself into a white lather across these areas and flow down the horse's legs.

If a horse is not sweating up after it resumes work after its summer break, it may be down to the following possibilities: the horse may have been doing some exercise in its stable during the break preventing excessive condition. It may also have a poor appetite or suffer from ailments in digestive system, resulting in poor nutritional absorption, therefore failing to put on weight.

The sweating of horses is related to seasonal and weather changes. They perspire when it is hot sweat less when it cools. The amount of sweat that oozes out during morning workouts correlates with the amount of works horses have done beforehand. Some horses sweat all over as they walk to the track because they may have done just trotting beforehand or been on the "horse walker" machine.

It takes a bit of knowing, but it is possible to assess the condition of a racehorse by the amount it sweats at any given time. Only by repeated observation can we make an accurate evaluation.