What is a cold sweat?

A cold sweat is sweating that comes with cool, clammy, and often pale skin, unlike the warm sweating of a hot day. It reflects a surge of the sympathetic nervous system, which turns on sweat glands while also narrowing skin blood vessels, so the skin sweats and cools at the same time.

What causes cold sweats?

Common triggers include severe pain, fear or panic, low blood sugar, a drop in blood pressure or shock, heart problems, fainting, and strong nausea. They all share a common thread: strong activation of the body's fight-or-flight nervous system rather than a response to heat.

Are cold sweats a sign of a heart attack?

They can be. A cold sweat (diaphoresis) is a recognized feature of a heart attack, and in people with chest pain it roughly doubles the likelihood of myocardial infarction. A sudden cold sweat with chest pain, pressure radiating to the arm or jaw, or severe shortness of breath should be treated as an emergency.

Why do cold sweats happen with low blood sugar?

As blood glucose falls toward about 70 mg/dL, the body releases adrenaline and activates the sympathetic nervous system. Sweating is one of the earliest and most common autonomic warning signs, along with shakiness, palpitations, and hunger. It is a cue to treat the low blood sugar.

When should I worry about a cold sweat?

Seek urgent care for a cold sweat with chest pain or pressure, severe shortness of breath, fainting or near-fainting, confusion or slurred speech, signs of a severe allergic reaction, or a low blood sugar that does not respond to treatment. Occasional cold sweats from fright, pain, or a near-faint are usually not dangerous.

Is this page medical advice?

No. It is an educational summary of the physiology and common causes of cold sweats, drawn from published sources. It cannot diagnose the cause of any single episode, and sudden or alarming cold sweats should be assessed by a clinician.

Research

Cold Sweats: What They Are and Why They Happen

A cold sweat is a familiar but odd experience: the skin turns damp and clammy while feeling cool and often pale, unlike the warm flush of sweating on a hot day. The difference is in the trigger. Ordinary sweating is a response to heat, whereas a cold sweat is driven by a surge of the sympathetic nervous system, the body's fight-or-flight system, in response to pain, fear, a drop in blood sugar, or a fall in blood pressure. This page explains the physiology and the situations in which cold sweats appear. It is educational and is not medical advice, and some causes of a sudden cold sweat are medical emergencies.

By the Sweat Explained Editorial Team · Published 2026-07-20 · Last reviewed 2026-07-20 · Educational information, not medical advice.

Key statistics at a glance

Sympathetic surge
cold sweats reflect fight-or-flight sympathetic activation rather than a heat load, which is why they feel different from ordinary sweating
Shibasaki & Crandall 2010 (Front Biosci)
< 70 mg/dL
plasma glucose (about 3.9 mmol/L) around which the body triggers autonomic warning symptoms, including sweating
Cryer 2013 (N Engl J Med)
~2x
diaphoresis (a cold sweat) roughly doubles the likelihood of acute myocardial infarction in people with chest pain (positive likelihood ratio near 2)
Swap & Nagurney 2005 (JAMA)
Pallor + sweat
the pale, sweaty, nauseated prodrome that commonly precedes a vasovagal faint reflects the same autonomic shift
Wieling 2009 (Brain)

What a cold sweat actually is

Clinically, sweating is called diaphoresis, and a cold sweat is diaphoresis combined with cool, clammy, often pale skin. That combination is the tell-tale sign. In heat-driven sweating the skin is warm and blood vessels are widened, because the goal is to lose heat. In a cold sweat the skin is cool and pale, because the same nervous-system signal that turns the sweat glands on is also narrowing blood vessels near the surface.

So a cold sweat is not a temperature-control response at all. It is a byproduct of the body's alarm system switching on. Recognizing that distinction is useful, because it explains why cold sweats tend to come with other alarm-system features, such as a racing heart, nausea, or lightheadedness, rather than with feeling hot.

The physiology: a fight-or-flight response

Sweat glands are controlled by the sympathetic nervous system. Under stress or threat, the sympathetic system fires and the adrenal glands release adrenaline, preparing the body to respond. Eccrine sweat glands, which are driven by the chemical messenger acetylcholine, switch on and produce sweat (Shibasaki & Crandall 2010). At the same time, small blood vessels in the skin constrict, shifting blood toward the core and muscles.

The result is the signature of a cold sweat: sweat on the surface, but skin that is pale and cool because less warm blood is flowing through it. This is why a sudden shock, severe pain, or a plunge in blood pressure can leave someone clammy and gray rather than flushed. The sweat and the coolness are two arms of the same reflex.

Common situations that cause cold sweats

Cold sweats appear whenever the sympathetic system is strongly activated. Common contexts described in the clinical literature include:

Severe pain. Intense pain, such as from an injury, kidney stone, or heart attack, can trigger a strong sympathetic response and a cold sweat.
Fear, anxiety, or panic. Acute fear and panic attacks activate fight-or-flight, which can produce sudden clammy sweating along with a pounding heart.
Low blood sugar (hypoglycemia). As glucose falls, the body releases counter-regulatory hormones and sweating is one of the earliest and most common warning signs (Cryer 2013).
Low blood pressure or shock. A sharp drop in blood pressure, from blood loss, severe infection, or a strong allergic reaction, triggers sympathetic activation and a cold, clammy sweat.
Heart problems. Diaphoresis is a recognized feature of a heart attack; in people with chest pain it roughly doubles the likelihood of myocardial infarction (Swap & Nagurney 2005).
Fainting (vasovagal syncope). The prelude to a common faint often includes pallor, nausea, and a cold sweat as autonomic control shifts (Wieling 2009).
Nausea and vomiting. Strong nausea from many causes is frequently accompanied by a cold, clammy sweat.

A closer look at low blood sugar

Low blood sugar is one of the most clear-cut causes of a cold sweat, and it shows the physiology well. As plasma glucose falls toward roughly 70 mg/dL (about 3.9 mmol/L), the body mounts a defensive response, releasing hormones such as adrenaline and activating the sympathetic nervous system (Cryer 2013). Sweating is among the earliest and most common of these autonomic warning symptoms, alongside tremor, palpitations, hunger, and anxiety.

This is especially relevant for people who take insulin or certain other diabetes medications, in whom sweating can be an important early cue of a low. Because sweating here is a warning sign rather than the problem itself, the response to it is to treat the underlying low blood sugar. Anyone whose sweating is tied to episodes of shakiness, confusion, or hunger should discuss it with their clinician.

When a cold sweat needs urgent attention

Most cold sweats are brief and have an obvious cause, such as a fright, a painful moment, or a near-faint, and they pass quickly. But because the same reflex accompanies some serious conditions, certain patterns deserve urgent medical attention. A sudden cold sweat with chest pain, pressure, or pain spreading to the arm, jaw, or back, with severe shortness of breath, with fainting or near-fainting, or with signs of a severe allergic reaction should be treated as an emergency.

Similarly, a cold sweat with confusion, slurred speech, or weakness, or one that accompanies a known low blood sugar that does not respond to treatment, warrants immediate help. These are red flags precisely because a cold sweat can be the body's alarm signaling a heart, circulation, or metabolic emergency. This page is educational and cannot assess any individual; when in doubt, seek care.

What this means in plain terms

A cold sweat is the body's alarm system leaving a visible mark: sweat from an activated sympathetic response, and cool, pale skin because blood vessels have narrowed at the same time. On its own, an occasional cold sweat from fear, pain, or a near-faint is common and not dangerous. What matters is the company it keeps, chest pain, breathlessness, fainting, confusion, or a low blood sugar that will not correct, because those combinations can signal something urgent.

Understanding the mechanism turns a strange sensation into something interpretable. This page describes physiology and general patterns; it is not a diagnosis and cannot tell you the cause of any single episode. Persistent, unexplained, or alarming cold sweats should be evaluated by a clinician.

Methodology and limitations

This page draws on peer-reviewed sources: a review of the mechanisms and control of eccrine sweating (Shibasaki & Crandall, Front Biosci 2010), a review of glucose counter-regulation and hypoglycemia symptoms (Cryer, N Engl J Med 2013), a meta-analysis of chest pain history in suspected acute coronary syndromes (Swap & Nagurney, JAMA 2005), a review of the physiology of syncope symptoms (Wieling et al., Brain 2009), and a clinical practice guideline on hypoglycemic disorders (Cryer et al., J Clin Endocrinol Metab 2009). The likelihood-ratio figure for diaphoresis and the hypoglycemia threshold were traced to those sources.

Limitations: cold sweat is a descriptive term rather than a single diagnosis, and the causes range from harmless to life-threatening, so the associations here are general patterns, not rules for any individual. The likelihood ratio for diaphoresis in myocardial infarction reflects specific study populations of people with chest pain and does not apply to sweating in isolation. This page is educational and is not medical advice; sudden or alarming cold sweats, especially with chest pain, breathlessness, fainting, or confusion, need urgent medical assessment.

Frequently asked questions

What is a cold sweat?: A cold sweat is sweating that comes with cool, clammy, and often pale skin, unlike the warm sweating of a hot day. It reflects a surge of the sympathetic nervous system, which turns on sweat glands while also narrowing skin blood vessels, so the skin sweats and cools at the same time.
What causes cold sweats?: Common triggers include severe pain, fear or panic, low blood sugar, a drop in blood pressure or shock, heart problems, fainting, and strong nausea. They all share a common thread: strong activation of the body's fight-or-flight nervous system rather than a response to heat.
Are cold sweats a sign of a heart attack?: They can be. A cold sweat (diaphoresis) is a recognized feature of a heart attack, and in people with chest pain it roughly doubles the likelihood of myocardial infarction. A sudden cold sweat with chest pain, pressure radiating to the arm or jaw, or severe shortness of breath should be treated as an emergency.
Why do cold sweats happen with low blood sugar?: As blood glucose falls toward about 70 mg/dL, the body releases adrenaline and activates the sympathetic nervous system. Sweating is one of the earliest and most common autonomic warning signs, along with shakiness, palpitations, and hunger. It is a cue to treat the low blood sugar.
When should I worry about a cold sweat?: Seek urgent care for a cold sweat with chest pain or pressure, severe shortness of breath, fainting or near-fainting, confusion or slurred speech, signs of a severe allergic reaction, or a low blood sugar that does not respond to treatment. Occasional cold sweats from fright, pain, or a near-faint are usually not dangerous.
Is this page medical advice?: No. It is an educational summary of the physiology and common causes of cold sweats, drawn from published sources. It cannot diagnose the cause of any single episode, and sudden or alarming cold sweats should be assessed by a clinician.

Sources

Primary peer-reviewed studies and official sources first, then reviews and institutional framing (secondary).

Shibasaki M, Crandall CG. Mechanisms and controllers of eccrine sweating in humans. Front Biosci (Schol Ed). 2010;2(2):685-696. Reviews sympathetic (cholinergic) control of eccrine sweating. Journal
Cryer PE. Mechanisms of hypoglycemia-associated autonomic failure in diabetes. N Engl J Med. 2013;369(4):362-372. Sweating as an autonomic warning symptom of hypoglycemia. Journal
Swap CJ, Nagurney JT. Value and limitations of chest pain history in the evaluation of patients with suspected acute coronary syndromes. JAMA. 2005;294(20):2623-2629. Diaphoresis positive likelihood ratio near 2 for myocardial infarction. Journal
Wieling W, Thijs RD, van Dijk N, et al. Symptoms and signs of syncope: a review of the link between physiology and clinical clues. Brain. 2009;132(Pt 10):2630-2642. Pallor and diaphoresis in the vasovagal prodrome. (secondary) Journal
Cryer PE, Axelrod L, Grossman AB, et al. Evaluation and management of adult hypoglycemic disorders: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2009;94(3):709-728. Autonomic symptoms of hypoglycemia, including sweating. (secondary) Journal

How to cite this page

Sweat Explained. Cold Sweats: What They Are and Why They Happen. Published 2026-07-20; last reviewed 2026-07-20. Available at: https://sweatexplained.com/research/cold-sweats-causes-and-physiology

Please cite the original studies for the underlying figures. Journalists are welcome to link to this page; the charts are original renderings of the cited data.