The phrase “break out in a cold sweat” generally means that one is scared, nervous, anxious, or terrified. More literally, it refers to sweating which occurs due to some factor other than increased body heat or physical exertion. This can be due to any of the aforementioned reasons, or due to illness of some sort.
To “break out in a cold sweat” can be taken both literally and figuratively. Sometimes when one becomes very frightened or nervous, sweating can occur. Other times this phrase is used as a turn of speech in order to imply that someone was feeling these emotions, whether or not a physical sweating response occurred. Symptoms often occur alongside sweating, including rapid heart rate, tremor, anxiety, dizziness, and sometimes fainting.
Most commonly, the phrase is used figuratively rather than literally. When one says that he or she broke out in a cold sweat, it is generally only meant to imply that the person was scared, anxious, frightened, or nervous. An actual sweat does not generally occur unless these feelings are prolonged. It is also usually meant to relate to dread or anticipation of an upcoming unpleasant event rather than a sudden and unexpected fright. The cold sweat occurs while the person is waiting for the threat or perceived threat to arrive.
Feeling scared or nervous may also cause a literal feeling of heat, combined with rapid heart rhythms which may lead to sweating. This is one possible explanation of where the phrase originated. In a more literal sense, a high fever may also lead to the feeling of breaking out in a sweat because the internal temperature is overheated, but the skin may feel chilled or cold.
A cold sweat may also include any unexplained sweating which occurs when the temperature does not warrant it. This can be caused by glandular conditions within the body, although sometimes a cause is never found. Those who find themselves sweating more than most should consult a doctor.
Sometimes when a person breaks out in a cold sweat, it can be a sign of a serious and life threatening condition. For instance, it is not uncommon for heart attack victims to sweat profusely during the episode. Medical attention should be sought right away if sweating occurs along with shortness of breath, chest pain, tightness in the chest, or any other troublesome symptoms.