How the Nervous System Controls Thermoregulation
Your body's temperature is carefully monitored and maintained by a small, but vital, region of the brain called the hypothalamus, which acts as your body’s thermostat. This part of the brain is the control center for thermoregulation, and it constantly receives information from nerves in the skin and from receptors in the blood about your current body temperature.
When the hypothalamus detects that your core temperature has dropped below its desired set point—either because of a cold environment or a fever—it triggers a series of involuntary responses via the nervous system. The hypothalamus sends signals through the nervous system to the skeletal muscles, causing them to contract and relax rapidly, which is the physical sensation of shivering. This rapid muscle activity expends energy and generates heat, effectively warming the body from the inside out.
Additionally, the sympathetic nervous system, a part of the autonomic nervous system, plays a key role by causing blood vessels in the skin to constrict. This is known as vasoconstriction and it reduces blood flow to the skin, minimizing heat loss to the external environment. This is why a person with chills often looks pale or feels cold to the touch, as blood is diverted to the core to protect vital organs.
Psychological Chills: The Fight-or-Flight Response
Beyond physical temperature regulation, the nervous system can also trigger chills in response to intense psychological states. The 'fight-or-flight' response, activated by the nervous system during moments of fear, stress, or excitement, causes a surge of adrenaline and other hormones. This can result in chills, shivers, or goosebumps, as the body prepares for a perceived threat. In this context, the chills are not an attempt to regulate temperature but are a byproduct of the body's heightened state of alert.
The Immune System's Role in Causing Chills
While the nervous system executes the shivering, the immune system is often the system that initiates the process during an illness. When the body detects a foreign invader, such as a virus or bacteria, the immune system launches a defense. As part of this defense, it releases chemicals called pyrogens.
Pyrogens travel to the hypothalamus and signal it to raise the body's temperature set point. This change in the brain's thermostat is the primary cause of a fever. Because the body's current temperature is now lower than the new, higher set point, the hypothalamus perceives the body as being too cold. It then activates the nervous system to trigger shivering and vasoconstriction to generate heat and bring the temperature up to the new, elevated level. This process is the primary reason why you often experience chills right before or during a fever.
- Pyrogen Release: The immune system releases pyrogens, which act as fever-inducing agents.
- Thermostat Reset: The pyrogens cause the hypothalamus to increase its temperature set point.
- Body Perceived as Cold: The body's current temperature is now below the new, higher set point, making you feel cold.
- Nervous System Activation: The hypothalamus activates the nervous system, initiating shivering to generate heat.
A Comparison of Chills from Different Body Systems
Understanding the distinction between nervous and immune-driven chills can help in recognizing the underlying cause.
| Feature | Chills from Nervous System (Psychological) | Chills from Immune System (Infection/Fever) |
|---|---|---|
| Trigger | Intense emotions (fear, anxiety, excitement), sudden temperature changes, or low blood sugar. | Response to pathogens like viruses or bacteria, stimulating the release of pyrogens. |
| Mechanism | Release of stress hormones like adrenaline, activating the fight-or-flight response. | Immune cells release pyrogens that signal the hypothalamus to raise the body's temperature set point. |
| Primary Goal | Part of a primal, automatic psychological response; not primarily for heat regulation. | Adaptive defense mechanism to fight infection by raising core body temperature. |
| Accompanying Symptoms | May include sweating, heart palpitations, or panic. | Often accompanied by fever, fatigue, body aches, and other symptoms of illness. |
| Fever Present | No, or a subfebrile temperature. | Yes, a true fever is typically present or developing. |
Other Systems That Can Cause Chills
While the nervous and immune systems are the main culprits, other body systems can also be involved in conditions that cause chills.
The Endocrine System
- Hypothyroidism: An underactive thyroid gland leads to a slower metabolism and reduced heat production, making a person more sensitive to cold and prone to chills.
- Hypoglycemia: Low blood sugar triggers the release of stress hormones, which can cause shaking and chills.
- Menopause: Hormonal shifts during menopause can disrupt the hypothalamus, leading to vasomotor symptoms like hot flashes or chills.
The Circulatory System
- Anemia: A deficiency in red blood cells or hemoglobin impairs oxygen transport throughout the body. The resulting lack of oxygen can cause a sensation of cold and lead to chills.
- Hypotension: A sudden drop in blood pressure can decrease blood flow to the extremities, leading to a cold sensation and shivering.
Conclusion: A Collaborative Effort
Chills are not an isolated event but a coordinated response involving multiple body systems. The process typically begins with the immune system identifying a threat and releasing chemical signals. The nervous system then receives these signals, processes them through the brain's thermoregulatory center, and activates the muscular system to shiver and generate heat. Meanwhile, the circulatory system adjusts blood flow to conserve warmth. In cases of emotional stress or endocrine disorders, the process can be initiated directly through neural or hormonal pathways without an immune trigger. This interconnected response highlights how the body works seamlessly to maintain a stable internal environment, a critical process known as homeostasis.
Ultimately, understanding the complex, multi-systemic origins of chills can help individuals recognize when their body is simply adjusting to a cold room and when it is signaling a more serious underlying issue that requires medical attention, based on information from the Mayo Clinic and other sources.
