Experiencing warmth and redness in your knees, especially when standing, is a common sensation that can sometimes cause concern. While these symptoms don’t always signify a serious problem, they can arise from various physiological processes or indicate underlying medical conditions. This article explores the different reasons why your knees might become hot and red upon standing, from normal bodily functions to more significant health issues.
Normal Physiological Responses
The human body possesses mechanisms to regulate blood flow, which explains why knees might temporarily become warm and red when standing. When you transition to a standing position, gravity causes blood to pool in the lower extremities. As blood pools, the body responds by dilating local blood vessels, a process known as vasodilation, to accommodate the increased volume and ensure proper circulation. This expansion of blood vessels near the skin’s surface results in warmth and redness.
Additionally, recent physical activity, such as exercise or prolonged walking, can increase metabolic activity in the knee’s muscles and tissues. This heightened activity generates heat, and the body’s natural cooling mechanisms, involving increased blood flow, contribute to the temporary warmth and redness.
Inflammatory Joint Conditions
Inflammation is the body’s natural protective response to injury or infection, characterized by heat, redness, swelling, and pain. When this process affects the knee joint, these signs are noticeable and often worsen with weight-bearing activities like standing. Several joint conditions commonly lead to such inflammatory reactions.
Arthritis
Arthritis is a frequent cause of knee inflammation. In osteoarthritis, cartilage wears away, leading to bone-on-bone friction and inflammation, which causes warmth and redness, especially during acute flares. Rheumatoid arthritis, an autoimmune disease, involves the immune system attacking the joint lining, or synovium. This causes chronic inflammation, pain, stiffness, and heat and redness in multiple joints, often symmetrically. Gout, another form of arthritis, results from uric acid crystal accumulation in a joint. This triggers sudden, severe inflammatory attacks that make the knee intensely hot, red, and painful.
Bursitis
Bursitis is the inflammation of bursae, small fluid-filled sacs that cushion joints. The knee has several bursae that can become inflamed from repetitive motion, prolonged kneeling, or direct pressure. This inflammation leads to localized heat, redness, tenderness, and swelling over the affected bursa.
Tendonitis
Tendonitis, or tendinopathy, is the inflammation or irritation of a tendon, the thick fibrous cords attaching muscle to bone. Overuse or injury to knee tendons, such as the patellar or quadriceps tendon, can cause localized warmth, redness, and pain, particularly with movement or weight bearing.
Infections and Other Medical Conditions
While less common than inflammatory joint conditions, certain infections and other medical issues can also manifest as hot and red knees, often requiring prompt medical attention.
Cellulitis
Cellulitis, a bacterial skin infection, frequently causes widespread redness, warmth, swelling, and tenderness. It can occur around the knee and may be accompanied by systemic symptoms like fever or chills.
Deep Vein Thrombosis (DVT)
Deep vein thrombosis (DVT) can present with warmth and redness, typically in one leg, though less commonly localized solely to the knee. DVT involves a blood clot in a deep vein, often in the thigh or calf, leading to pain, swelling, warmth, and skin discoloration. This condition is a medical emergency due to the risk of the clot traveling to the lungs.
Other Systemic Conditions
In rarer instances, systemic autoimmune diseases like lupus can cause joint inflammation, leading to warmth and redness during flares. Vasculitis, inflammation of blood vessels, can also present with joint symptoms.
When to Seek Professional Medical Advice
While some instances of hot and red knees are benign, certain symptoms warrant prompt medical evaluation. Seek medical advice if you experience:
Severe pain that prevents you from bearing weight on the knee.
Rapid onset or worsening of symptoms, especially if accompanied by significant swelling or bruising.
Fever, chills, or a general feeling of being unwell alongside knee symptoms, suggesting a possible infection.
Only one knee is affected without any obvious cause, or if symptoms persist or worsen despite rest.
Any suspicion of an infection, such as cellulitis, or a deep vein thrombosis, which can present with localized warmth and redness.
Only a qualified healthcare provider can accurately diagnose the cause of your symptoms and recommend the appropriate course of action.