What is Calor?
Calor, the Latin term for heat, is one of the classic signs of inflammation. It refers to the localized warmth or elevated temperature in the affected area, resulting from the body's immune response to tissue damage or infection.
The Cardinal Signs of Inflammation
Calor is one of the five cardinal signs of inflammation, first described by Celsus, with a fifth added by Galen [3]. These are rubor (redness), calor (heat), tumor (swelling), dolor (pain), and functio laesa (loss of function) [2, 3]. These signs are interconnected and represent the body's immediate response to injury or threat [2, 3].
The Pathophysiology Behind Calor
The heat of acute inflammation is a key part of the body's defense mechanism. Injury or pathogens trigger the release of chemical mediators like prostaglandins, histamine, and bradykinin [2, 4]. These mediators cause vasodilation, increasing local blood flow (hyperemia) and bringing warm blood to the damaged tissue, which raises its temperature [2].
The Role of Prostaglandins
Prostaglandins are lipid compounds synthesized by cyclooxygenases (COX-1 and COX-2) and are vital to calor [1]. They contribute by causing vasodilation, increasing blood flow and heat, and can also sensitize local nerve endings [1, 2]. More details are available from {Link: National Institutes of Health https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3081099/} [1].
Acute vs. Chronic Inflammation and Calor
Calor is most prominent in acute inflammation, a short-term response. In chronic inflammation, the signs are more subtle, and low-grade calor can indicate underlying issues [2].
| Feature | Acute Inflammation | Chronic Inflammation |
|---|---|---|
| Onset | Fast, within minutes to hours [2] | Slow, develops over time [2] |
| Duration | Short-term (days) [2] | Long-term (months to years) [2] |
| Cardinal Signs | All five are typically present and prominent [3] | May be subtle, localized, or absent; loss of function can be significant [2] |
| Key Cells | Neutrophils [4] | Macrophages, lymphocytes, plasma cells [4] |
| Primary Cause | Injury, infection, foreign irritant [2] | Persistent infection, autoimmune disease, prolonged exposure to irritants [2] |
| Clinical Example | Sprained ankle, bacterial infection [3] | Rheumatoid arthritis, psoriasis [2] |
How Calor Helps the Body
Calor is beneficial as the elevated temperature may enhance immune cell activity, aid in defense and repair, and potentially inhibit pathogen growth [2]. Along with other signs, it signals the need to protect the injured area, facilitating healing [3].
Conclusion
Calor in acute inflammation is the localized heat at an injury or infection site [2]. It is a fundamental part of the body's defense and results from vasodilation driven by mediators like prostaglandins [1, 2]. Understanding its mechanism, especially in acute cases, reveals how the body initiates healing and fights pathogens [2]. Recognizing this sign is key to understanding the body's protective abilities [3].
