The feeling of “hot blood” or an internal surge of heat is a common but often confusing sensation, technically known as flushing. While the body’s core temperature is tightly regulated and remains stable, this sensation arises from changes in blood flow close to the skin’s surface. This warmth is the physical manifestation of the body actively attempting to maintain its internal temperature balance.
How the Body Creates the Sensation of Heat
The sensation of internal heat is primarily a result of the body’s thermoregulatory system attempting to cool itself. This cooling process is managed by the hypothalamus, a small region in the brain that acts as the body’s thermostat. When the hypothalamus detects an increase in temperature, or is chemically signaled, it initiates a mechanism called vasodilation.
Vasodilation is the widening of blood vessels, particularly the tiny capillaries located just beneath the skin. This action increases blood flow to the body’s periphery, bringing warm blood from the core closer to the surrounding environment. The increased volume and proximity of warm blood to the skin surface causes the subjective feeling of heat and often visible redness or flushing. Heat then radiates from the skin into the air, effectively cooling the blood before it returns to the body’s core. This natural response can also be triggered inappropriately by various internal chemical signals.
Non-Infectious Triggers for Feeling Hot
One of the most frequent non-infectious causes of sudden internal heat is hormonal fluctuation, often experienced as hot flashes during menopause. A decline in estrogen levels can affect the hypothalamus, essentially narrowing the body’s “thermoneutral zone.” This means the brain’s thermostat becomes hypersensitive and triggers a heat-dissipation response, like sweating and vasodilation, in reaction to even a minor increase in core temperature.
Acute stress and anxiety also trigger a wave of heat through the sympathetic nervous system. The “fight-or-flight” response releases hormones like adrenaline (epinephrine), which causes a temporary increase in heart rate and blood vessel dilation. This rush of blood near the skin’s surface leads to the sensation of flushing and warmth, particularly in the face and chest.
Certain foods and beverages can mimic this internal heat response without raising the actual body temperature. The chemical capsaicin, found in chili peppers, binds to specific pain receptors that are also activated by actual heat. This binding tricks the brain into perceiving a burning sensation, prompting the natural cooling responses of flushing and sweating.
Prescription medications represent another common source of flushing, as many drugs directly affect the cardiovascular or nervous systems. Examples include certain antidepressants, calcium channel blockers, and hormonal therapies like Tamoxifen. These substances can induce vasodilation or interfere with neurotransmitters that help regulate temperature, leading to a feeling of being excessively warm.
Systemic Conditions That Cause Internal Heat
A measured fever represents a systemic condition where the body’s internal thermostat is intentionally reset to a higher temperature. This process is initiated when immune cells release pyrogens in response to an infection. These pyrogens travel to the hypothalamus, stimulating the production of a chemical messenger that raises the hypothalamic set point. This causes the body to actively generate and conserve heat until the new, higher temperature is reached.
Chronic inflammatory conditions, such as autoimmune diseases like Lupus or Rheumatoid Arthritis, can also cause a persistent feeling of being hot. In these cases, the immune system’s constant activation leads to a low-grade release of the same pyrogenic cytokines that cause fever. This systemic inflammation can result in recurrent, low-grade fevers or a generalized feeling of warmth, even when a high fever is not present.
Endocrine disorders, especially hyperthyroidism, directly increase the body’s basal metabolic rate (BMR). An overactive thyroid gland produces an excess of thyroid hormones. These hormones increase the rate of oxygen consumption and energy expenditure in most tissues, causing the body to generate more heat overall. This metabolic overdrive results in a chronic feeling of heat intolerance and increased sweating.
When to Consult a Healthcare Provider
While many instances of feeling hot are temporary and harmless, certain accompanying symptoms warrant a medical evaluation. You should consult a healthcare provider if the flushing or heat sensation is unexplained, persistent, or interferes with daily life or sleep.
Immediate medical attention is necessary if the heat sensation is accompanied by signs of a severe systemic reaction. These red flag symptoms include:
- A high fever of 103°F or higher.
- Severe headache or neck stiffness.
- Mental confusion.
- Persistent vomiting.
- Difficulty breathing or chest pain.
- A widespread, non-blanching skin rash.
Seek evaluation if the internal heat is accompanied by unexplained weight loss, chronic diarrhea, a racing heart, or a tremor, as these can be signs of underlying endocrine or systemic disease. It is also important to notify a doctor if the sensation begins shortly after starting a new medication, as a dosage adjustment or alternative drug may be required.